Build/Test Tools: Simplify redundant PHPUnit shim for `setExpectedException()`.

PHPUnit 6 deprecated the `setExpectedException()` method in favor of the `expectException()`, `expectExceptionMessage()`, and `expectExceptionCode()` methods.

`WP_UnitTestCase_Base::setExpectedException()` backfilled the old method. As the PHPUnit Polyfills have a polyfill for the ''new'' method, this backfill can now be simplified.

This backfill ''should'' be removed in a future iteration, but is, for now, left in place so as not to break backward compatibility for plugin/theme test suites which extend the WP native test suite for their integration tests.

Follow-up to [48996], [48997], [51559-51561].

Props jrf.
See #46149.
Built from https://develop.svn.wordpress.org/trunk@51562


git-svn-id: http://core.svn.wordpress.org/trunk@51173 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-51561';
+$wp_version = '5.9-alpha-51562';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.