docs: remove migration-ngcc guide (#33727)

PR Close #33727

.github/CODEOWNERS

@@ -887,7 +887,6 @@ testing/**                                                      @angular/fw-test
 /aio/content/guide/migration-injectable.md                      @angular/fw-docs-packaging @angular/framework-global-approvers @angular/framework-global-approvers-for-docs-only-changes
 /aio/content/guide/migration-localize.md                        @angular/fw-docs-packaging @angular/framework-global-approvers @angular/framework-global-approvers-for-docs-only-changes
 /aio/content/guide/migration-module-with-providers.md           @angular/fw-docs-packaging @angular/framework-global-approvers @angular/framework-global-approvers-for-docs-only-changes
-/aio/content/guide/migration-ngcc.md                            @angular/fw-docs-packaging @angular/framework-global-approvers @angular/framework-global-approvers-for-docs-only-changes
 /aio/content/guide/updating-to-version-9.md                     @angular/fw-docs-packaging @angular/framework-global-approvers @angular/framework-global-approvers-for-docs-only-changes
 /aio/content/guide/ivy-compatibility.md                         @angular/fw-docs-packaging @angular/framework-global-approvers @angular/framework-global-approvers-for-docs-only-changes
 /aio/content/guide/ivy-compatibility-examples.md                     @angular/fw-docs-packaging @angular/framework-global-approvers @angular/framework-global-approvers-for-docs-only-changes

aio/content/guide/migration-ngcc.md

@@ -1,79 +0,0 @@
-# Migration to `ngcc` npm `postinstall` script
-
-## What does this schematic do?
-
-This schematic adds an [Angular compatibility compiler](guide/ngcc), or `ngcc`, invocation to npm/yarn's `postinstall` script in the `package.json` of an Angular CLI workspace.
-This script is invoked after each execution of `npm install` and modifies `node_modules` by converting any found Angular libraries to a format that is compatible with Angular version 9.
-
-An example diff might look like the following:
-
-**Before:**
-
-```json
-  "scripts": {
-    "ng": "ng",
-    "start": "ng serve",
-    "build": "ng build",
-    "test": "ng test",
-    "lint": "ng lint",
-    "e2e": "ng e2e"
-  },
-```
-
-**After:**
-
-```json
-  "scripts": {
-    "ng": "ng",
-    "start": "ng serve",
-    "build": "ng build",
-    "test": "ng test",
-    "lint": "ng lint",
-    "e2e": "ng e2e",
-    "postinstall": "ngcc --properties es2015 browser module main --first-only --create-ivy-entry-points"
-  },
-```
-
-If the `package.json` already contains a `postinstall` script, then the `ngcc` invocation will be prepended to the current command:
-
-**Before:**
-```json
-  "scripts": {
-    ...
-    "postinstall": "some-command"
-  },
-```
-
-**After:**
-```json
-  "scripts": {
-    ...
-    "postinstall": "ngcc --properties es2015 browser module main --first-only --create-ivy-entry-points && some-command"
-  },
-```
-
-
-## Why is this migration necessary?
-
-This migration is a build performance optimization that enables `ngcc` to parallelize the compilation of npm libraries.
-An application build performed via CLI's `ng build` should succeed regardless of this `postinstall` script being installed, because the CLI has `ngcc` built-in.
-However, this built-in `ngcc` can't parallelize the compilation of multiple libraries, and therefore often takes considerably longer to run.
-
-
-## Can I customize the `ngcc` options in the `postinstall` script?
-
-By default the `postinstall` script invokes `ngcc` with options to compile only the most commonly needed library formats.
-For some projects, especially those that depend on the CommonJS distribution of Angular (for example, Angular Universal apps), it might be beneficial to modify the `postinstall` script to also compile the CommonJS distribution of the library:
-
-```json
-  "scripts": {
-    ...
-    "postinstall": "ngcc --properties es2015 browser module main --first-only --create-ivy-entry-points && ngcc --properties main --create-ivy-entry-points"
-  },
-```
-
-For the full set of options run `npx ngcc --help` or `yarn ngcc --help`.
-
-## Will libraries compiled with `ngcc` still be compatible with Angular version 8?
-
-Yes, the migration causes `ngcc` to be invoked with the `--create-ivy-entry-points` flag, which ensures that the `ngcc` compilation is non-destructive, so the same `node_modules` can be used with Angular version 8 and version 9.

aio/content/guide/updating-to-version-9.md

@@ -97,4 +97,3 @@ Read about the migrations the CLI handles for you automatically:
 - [Migrating dynamic queries](guide/migration-dynamic-flag)
 - [Migrating to the new `$localize` i18n support](guide/migration-localize)
 - [Migrating `ModuleWithProviders`](guide/migration-module-with-providers)
-- [Migrating to `ngcc` npm `postinstall` script](guide/migration-ngcc)