Remove jquery-scrollto-rails

Added in this commit when CI was merged into the main GitLab application. jquery-scrollto-rails has two major problems which (IMO) require its removal:

• Parts of the gem are licensed under the GPLv2. This is a violation of the GPL, as GPL cannot be used as a library for non-GPL software according to the FSF. The only other (non-development/non-test) gem in our Gemfile that has this problem is colorize, so complying with this requirement isn't particularly hard. (https://gitlab.com/gitlab-com/operations/issues/164#note_9313730, !3775 (merged)) It's also preventing us from enabling the license_finder gem so builds can ensure license compliance.
• It will block the upgrade to Rails 5 due to its dependency on railties "< 5". (See #14286 (moved))

cc: @DouweM @jschatz1 @rspeicher

mentioned in issue gitlab-com/operations#164 (closed)

Is there a suitable alternative? Because we do actually use it.

@connorshea @rspeicher couldn't we just take the JS lib out of it and plop it in our js directory ourselves? The lib itself is MIT ASAIK https://github.com/flesler/jquery.scrollTo/blob/master/LICENSE

@jschatz1 It looks like it was changed two years ago, so yeah we should just use the library itself. That simplifies things.

https://github.com/flesler/jquery.scrollTo/commit/0635bbf17ebddc3e0ace77827c91429f20f2ccee

Ok, that'll work.

Added frontend label

Milestone changed to 8.8

mentioned in issue #14286 (moved)

mentioned in merge request !4088 (merged)

Status changed to closed by commit 976a7052

mentioned in commit 976a7052

mentioned in commit c24cd968