Merge branch 'docs-clean-redirects-2022-01-12' into 'master'

Clean up docs redirects - 2022-01-12

See merge request gitlab-org/gitlab!78029

doc/administration/operations/cleaning_up_redis_sessions.md

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-redirect_to: 'index.md'
-remove_date: '2021-12-10'
----
-
-This document was moved to [another location](index.md).
-
-<!-- This redirect file can be deleted after 2021-12-10. -->
-<!-- Before deletion, see: https://docs.gitlab.com/ee/development/documentation/#move-or-rename-a-page -->

doc/development/snowplow/dictionary.md

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-redirect_to: 'https://metrics.gitlab.com/snowplow.html'
-remove_date: '2021-12-28'
----