Remove executable permissions on images to make docs lint happy

See merge request gitlab-org/gitlab-ce!14750

Fix error with GPG signature updater when commit was deleted

Closes #38890

See merge request gitlab-org/gitlab-ce!14749

Normalize LDAP user DNs (downcase and remove excess spaces)

See merge request gitlab-org/gitlab-ce!14697

[ci skip]

Remove old navigation CSS

See merge request gitlab-org/gitlab-ce!14573

I first attempted to extract logic from the code that normalizes DNs, but I was unsuccessful. This is a hack but it works.

Since that behavior changed, and is now under the malformed DN context.

Especially from the last attribute value.

Disabling some for now since this is based on `Net::LDAP::DN`.

for normalizing and parsing DNs