Don't enforce UTF-8 by default (Rails 6.0 default config)

Proposal

Shorten the URL for search any kind of issuables, Issues, Merge Requests, Epics, Milestones, even for Advanced Search.

Removes the UTF-8 workaround for IE5-8 prepared in Rails 3.0 through 5.2. This was missing in upgrading to Rails 6.0 (#19891).

• Before this change: https://gitlab.com/gitlab-org/gitlab/-/issues?scope=all&utf8=%E2%9C%93&state=opened&search=%22enforce+UTF-8%22
• After this change: https://gitlab.com/gitlab-org/gitlab/-/issues?scope=all&state=opened&search=%22enforce+UTF-8%22

Ref.

• https://github.com/rails/rails/pull/32125
• https://github.com/rails/rails/pull/32131