Remove entries of legacy Chrome image tags from the CI manifest

While !56 (merged) started to preserve the image tag for old Chrome versions once in 2017-09, !83 (merged) started to use an object storage (Amazon S3, since the inception to date (2021-03), cf. #42 (closed)) in 2018-03. 3 years passed after !83 (merged) and we can see good enough versions stored at https://s3.amazonaws.com/gitlab-google-chrome-stable/, so we can safely remove the entries of the image tag for old Chrome versions from .gitlab-ci.yml (cf. clean up the images themselves from the Registry, #8 (closed)).