Merge branch 'docs-clean-redirects-2021-08-18' into 'master'

Clean up docs redirects - 2021-08-18

See merge request gitlab-org/gitlab!68436

doc/development/testing_guide/end_to_end/environment_selection.md

----
-redirect_to: 'execution_context_selection.md'
-remove_date: '2021-08-14'
----
-
-This file was moved to [another location](execution_context_selection.md).
-
-<!-- This redirect file can be deleted after <2021-08-14>. -->
-<!-- Before deletion, see: https://docs.gitlab.com/ee/development/documentation/#move-or-rename-a-page -->