Unify to remove "This cop" from cop description in default.yml

Follow up rubocop/rubocop#10612.

config/default.yml

@@ -107,7 +107,7 @@ Rails/AddColumnIndex:
 
 Rails/AfterCommitOverride:
   Description: >-
-                  This cop enforces that there is only one call to `after_commit`
+                  Enforces that there is only one call to `after_commit`
                   (and its aliases - `after_create_commit`, `after_update_commit`,
                   and `after_destroy_commit`) with the same callback name per model.
   Enabled: 'pending'
@@ -691,7 +691,7 @@ Rails/RedundantReceiverInWithOptions:
   VersionAdded: '0.52'
 
 Rails/RedundantTravelBack:
-  Description: This cop checks for redundant `travel_back` calls.
+  Description: Checks for redundant `travel_back` calls.
   Enabled: pending
   VersionAdded: '2.12'
   Include:
@@ -809,7 +809,7 @@ Rails/SaveBang:
 
 Rails/SchemaComment:
   Description: >-
-    This cop enforces the use of the `comment` option when adding a new table or column
+    Enforces the use of the `comment` option when adding a new table or column
     to the database during a migration.
   Enabled: false
   VersionAdded: '2.13'

spec/project_spec.rb

@@ -20,6 +20,13 @@
         description = config[name]['Description']
         expect(description.nil?).to be(false)
         expect(description).not_to include("\n")
+
+        start_with_subject = description.match(/\AThis cop (?<verb>.+?) .*/)
+        suggestion = start_with_subject[:verb]&.capitalize if start_with_subject
+        suggestion ||= 'a verb'
+        expect(start_with_subject).to(
+          be_nil, "`Description` for `#{name}` should be started with `#{suggestion}` instead of `This cop ...`."
+        )
       end
     end