Stop generating comment about schema_migrations in structure files

As it is generally well-known, and we save the effort of not having to
make the schema cleaner multi-database aware

db/ci_structure.sql

@@ -42,6 +42,4 @@ ALTER TABLE ONLY ci_instance_variables
 ALTER TABLE ONLY schema_migrations
     ADD CONSTRAINT schema_migrations_pkey PRIMARY KEY (version);
 
-CREATE UNIQUE INDEX index_ci_instance_variables_on_key ON ci_instance_variables USING btree (key);-- schema_migrations.version information is no longer stored in this file,
--- but instead tracked in the db/schema_migrations directory
--- see https://gitlab.com/gitlab-org/gitlab/-/issues/218590 for details
+CREATE UNIQUE INDEX index_ci_instance_variables_on_key ON ci_instance_variables USING btree (key);

db/structure.sql

@@ -27961,6 +27961,4 @@ ALTER TABLE ONLY user_follow_users
     ADD CONSTRAINT user_follow_users_followee_id_fkey FOREIGN KEY (followee_id) REFERENCES users(id) ON DELETE CASCADE;
 
 ALTER TABLE ONLY user_follow_users
-    ADD CONSTRAINT user_follow_users_follower_id_fkey FOREIGN KEY (follower_id) REFERENCES users(id) ON DELETE CASCADE;-- schema_migrations.version information is no longer stored in this file,
--- but instead tracked in the db/schema_migrations directory
--- see https://gitlab.com/gitlab-org/gitlab/-/issues/218590 for details
+    ADD CONSTRAINT user_follow_users_follower_id_fkey FOREIGN KEY (follower_id) REFERENCES users(id) ON DELETE CASCADE;

lib/gitlab/database/schema_cleaner.rb

@@ -30,11 +30,7 @@ module Gitlab
         structure.gsub!(/\n{3,}/, "\n\n")
 
         io << structure.strip
-        io << <<~MSG
-          -- schema_migrations.version information is no longer stored in this file,
-          -- but instead tracked in the db/schema_migrations directory
-          -- see https://gitlab.com/gitlab-org/gitlab/-/issues/218590 for details
-        MSG
+        io << "\n"
 
         nil
       end

spec/fixtures/gitlab/database/structure_example_cleaned.sql

@@ -23,6 +23,4 @@ ALTER TABLE ONLY abuse_reports ALTER COLUMN id SET DEFAULT nextval('abuse_report
 ALTER TABLE ONLY abuse_reports
     ADD CONSTRAINT abuse_reports_pkey PRIMARY KEY (id);
 
-CREATE INDEX index_abuse_reports_on_user_id ON abuse_reports USING btree (user_id);-- schema_migrations.version information is no longer stored in this file,
--- but instead tracked in the db/schema_migrations directory
--- see https://gitlab.com/gitlab-org/gitlab/-/issues/218590 for details
+CREATE INDEX index_abuse_reports_on_user_id ON abuse_reports USING btree (user_id);