Add remove_date to redirects

In two MRs I forgot the remove_date entry, so the
redirect cleanup automation can't pick up these
redirect files.

doc/README.md

 ---
 redirect_to: 'index.md'
+remove_date: '2021-09-28'
 ---
 
 This document was moved to [another location](index.md).

doc/api/README.md

 ---
 redirect_to: 'index.md'
+remove_date: '2021-09-28'
 ---
 
 This document was moved to [another location](index.md).

doc/ci/README.md

 ---
 redirect_to: 'index.md'
+remove_date: '2021-09-28'
 ---
 
 This document was moved to [another location](index.md).

doc/ci/examples/README.md

 ---
 redirect_to: 'index.md'
+remove_date: '2021-09-28'
 ---
 
 This document was moved to [another location](index.md).

doc/ci/examples/deployment/README.md

 ---
 redirect_to: 'index.md'
+remove_date: '2021-09-28'
 ---
 
 This document was moved to [another location](index.md).

doc/ci/merge_request_pipelines/index.md

 ---
 redirect_to: '../pipelines/merge_request_pipelines.md'
+remove_date: '2021-09-29'
 ---
 
 This document was moved to [another location](../pipelines/merge_request_pipelines.md).

doc/ci/merge_request_pipelines/pipelines_for_merged_results/index.md

 ---
 redirect_to: '../../pipelines/pipelines_for_merged_results.md'
+remove_date: '2021-09-29'
 ---
 
 This document was moved to [another location](../../pipelines/pipelines_for_merged_results.md).

doc/ci/merge_request_pipelines/pipelines_for_merged_results/merge_trains/index.md

 ---
 redirect_to: '../../../pipelines/merge_trains.md'
+remove_date: '2021-09-29'
 ---
 
 This document was moved to [another location](../../../pipelines/merge_trains.md).

doc/ci/multi_project_pipelines.md

 ---
 redirect_to: 'pipelines/multi_project_pipelines.md'
+remove_date: '2021-09-29'
 ---
 
 This document was moved to [another location](pipelines/multi_project_pipelines.md).

doc/ci/parent_child_pipelines.md

 ---
 redirect_to: 'pipelines/parent_child_pipelines.md'
+remove_date: '2021-09-29'
 ---
 
 This document was moved to [another location](pipelines/parent_child_pipelines.md).

doc/ci/runners/README.md

 ---
 redirect_to: 'index.md'
+remove_date: '2021-09-28'
 ---
 
 This document was moved to [another location](index.md).

doc/ci/triggers/README.md

 ---
 redirect_to: 'index.md'
+remove_date: '2021-09-28'
 ---
 
 This document was moved to [another location](index.md).

doc/ci/variables/README.md

 ---
 redirect_to: 'index.md'
+remove_date: '2021-09-28'
 ---
 
 This document was moved to [another location](index.md).

doc/ci/yaml/README.md

 ---
 redirect_to: 'index.md'
+remove_date: '2021-09-28'
 ---
 
 This document was moved to [another location](index.md).

doc/development/README.md

 ---
 redirect_to: 'index.md'
+remove_date: '2021-09-28'
 ---
 
 This document was moved to [another location](index.md).

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).

doc/security/README.md

 ---
 redirect_to: 'index.md'
+remove_date: '2021-09-28'
 ---
 
 This document was moved to [another location](index.md).

doc/ssh/README.md

 ---
 redirect_to: 'index.md'
+remove_date: '2021-09-28'
 ---
 
 This document was moved to [another location](index.md).