Revert "FIX: Add missing unique index on user_id for user_profiles."

Oops `user_id` is the primary key.

This reverts commit 5478aa63ab.

app/models/user_profile.rb

@@ -11,7 +11,6 @@ class UserProfile < ActiveRecord::Base
   belongs_to :card_background_upload, class_name: "Upload"
   belongs_to :profile_background_upload, class_name: "Upload"
 
-  validates :user_id, uniqueness: true
   validates :bio_raw, length: { maximum: 3000 }
   validates :website, url: true, allow_blank: true, if: Proc.new { |c| c.new_record? || c.website_changed? }
   validates :user, presence: true

db/migrate/20190524040814_add_unique_index_user_id_on_user_profiles.rb

@@ -1,5 +0,0 @@
-class AddUniqueIndexUserIdOnUserProfiles < ActiveRecord::Migration[5.2]
-  def change
-    add_index :user_profiles, :user_id, unique: true
-  end
-end

spec/models/user_profile_spec.rb

@@ -40,7 +40,7 @@ describe UserProfile do
     end
 
     context "website validation" do
-      let(:user_profile) { Fabricate.build(:user_profile) }
+      let(:user_profile) { Fabricate.build(:user_profile, user: Fabricate(:user)) }
 
       it "should not allow invalid URLs" do
         user_profile.website = "http://https://google.com"