Resolve "Remove pages settings fix rake task after executing it on production"

What does this MR do?

!18386 (diffs) added a migration fixing pages access control setting for gitlab.com, this migration was already executed and all projects migrated.

So now we need to remove this migration as we planned: !18386 (comment 232450502)

The empty migration is left to avoid any problems with rolling back/reapplying migrations. It can be safely rerun:

./bin/rails db:migrate:redo VERSION=20191017045817
== 20191017045817 ScheduleFixGitlabComPagesAccessLevel: reverting =============
== 20191017045817 ScheduleFixGitlabComPagesAccessLevel: reverted (0.0000s) ====

== 20191017045817 ScheduleFixGitlabComPagesAccessLevel: migrating =============
== 20191017045817 ScheduleFixGitlabComPagesAccessLevel: migrated (0.0000s) ====

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #34018 (closed)