When we don't use the original `ApplicationHelper#avatar_icon` anymore, we
can just remove it (and its specs).

Closes #42800.

Callers expect a URL.

This fixes the avatars in commit lists when a user has no avatar and
Gravatar is disabled.

Closes #38715

If using gravatar.com, both plain_url and ssl_url in settings are now
served via HTTPS. Make this the default.

We don't want the locale to be set to Brazilian Portuguese for any subsequent
specs!

The locale code is turned into an asset path with an underscore
instead of a dash.

The language codes are transformed by `I18n.locale` into a code with a
dash. But the resources for translating are always stored in a path
using a `_` separating the language and the region code.

Signed-off-by: Rémy Coutable <remy@rymai.me>

Ran:
 - git format-patch v9.2.2..v9.2.5 --stdout > patchfile.patch
 - git checkout -b 9-2-5-security-patch origin/v9.2.2
 - git apply patchfile.patch
 - git commit
 - [Got the sha ref for the commit]
 - git checkout -b upstream-9-2-security master
 - git cherry-pick <SHA of the patchfile commit>
 - [Resolved conflicts]
 - git cherry-pick --continue

Ran:
 - git format-patch v9.2.2..v9.2.5 --stdout > patchfile.patch
 - git checkout -b 9-2-5-security-patch origin/v9.2.2
 - git apply patchfile.patch
 - git commit
 - [Got the sha ref for the commit]
 - git checkout -b upstream-9-2-security master
 - git cherry-pick <SHA of the patchfile commit>
 - [Resolved conflicts]
 - git cherry-pick --continue

Ran:
 - git format-patch v9.2.2..v9.2.5 --stdout > patchfile.patch
 - git checkout -b 9-2-5-security-patch origin/v9.2.2
 - git apply patchfile.patch
 - git commit
 - [Got the sha ref for the commit]
 - git checkout -b upstream-9-2-security master
 - git cherry-pick <SHA of the patchfile commit>
 - [Resolved conflicts]
 - git cherry-pick --continue

Because the post-processing of the rendered README is dependent on the
context (i.e. the current user), do the post-processing when the
README is being displayed.

This reverts commit cb10b725c8929b8b4460f89c9d96c773af39ba6b.

This reverts commit cb10b725c8929b8b4460f89c9d96c773af39ba6b.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/24036

This would fix long standing failures running tests on
my development machine, which set `Gitlab.config.gitlab.host`
to another host because it's not my local computer. Now I
finally cannot withstand it and decided to fix them once and
for all.