Upgrade sprockets and sprockets rails, remove quiet_assets

What does this MR do?

Upgrade Sprockets from 3.6.0 to 3.6.2.

Changelog: https://github.com/rails/sprockets/blob/3.x/CHANGELOG.md

Upgrade Sprockets Rails from 3.0.4 to 3.1.1.

Changelog: https://github.com/rails/sprockets-rails/compare/v3.0.4...v3.1.1

quiet_assets has been seemingly abandoned, and now sprockets-rails has the feature built-in!

The config was added in this PR: https://github.com/rails/sprockets-rails/pull/355

Working towards #14286 (moved).

• Tests
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together

cc: @rspeicher