Use native Hash#except, remove ActiveSupport 🐵-patch

[dduugg]

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Relates to #16190

Ruby 3.0 added Hash#except, so we no longer need the ActiveSupport monkey-patch.

Note that there was also a Hash#except! monkey-patch in the ActiveSupport module. The only usage that I could find was in livecheck/livecheck. I've refactored those away, and added strict typing to the file while I was there.

[dduugg]

I also found that we were using a Hash#slice! monkey-patch within a dev command, so I've refactored that out as well

[Bo98]

Thanks!

[MikeMcQuaid]

Thanks @dduugg!