Revert "Merge branch 'ps-add-sourcegraph-feature-flag-yml' into 'master'"

This reverts merge request !49442

config/feature_flags/development/sourcegraph.yml

----
-name: sourcegraph
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/16556
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/292199
-milestone: '12.5'
-type: development
-group: group::editor
-default_enabled: false