Remove pin comment from Auto DevOps templates

We do actually intend to pin to known tags from now on, to prevent
last-minute surprises from Docker image floating tag updates

lib/gitlab/ci/templates/Jobs/Browser-Performance-Testing.gitlab-ci.yml

 performance:
   stage: performance
-  # pin to a version matching the dind service, just to be safe
   image: docker:19.03.5
   allow_failure: true
   variables:
     DOCKER_TLS_CERTDIR: ""
   services:
-    # pin to a known working version until https://gitlab.com/gitlab-org/gitlab-runner/issues/6697 is fixed
     - docker:19.03.5-dind
   script:
     - |

lib/gitlab/ci/templates/Jobs/Build.gitlab-ci.yml

@@ -4,7 +4,6 @@ build:
   variables:
     DOCKER_TLS_CERTDIR: ""
   services:
-    # pin to a known working version until https://gitlab.com/gitlab-org/gitlab-runner/issues/6697 is fixed
     - docker:19.03.5-dind
   script:
     - |

lib/gitlab/ci/templates/Jobs/Code-Quality.gitlab-ci.yml

 code_quality:
   stage: test
-  # pin to a version matching the dind service, just to be safe
   image: docker:19.03.5
   allow_failure: true
   services:
-    # pin to a known working version until https://gitlab.com/gitlab-org/gitlab-runner/issues/6697 is fixed
     - docker:19.03.5-dind
   variables:
     DOCKER_DRIVER: overlay2