tap: revert caching Tap.reverse_tap_migrations_renames

[apainintheneck]

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This could cause problems if a tap is installed during the lifetime of the program which happens occasionally with Tap#ensure_installed!.

It also seems to be slow mainly because of intermediate arrays and Pathname objects that get created in Tap.each. Maybe that should be optimized instead.

As discussed in #16791 (comment)

[MikeMcQuaid]

Thanks @apainintheneck!

This could cause problems if a tap is installed during the lifetime of the program which happens occasionally with Tap#ensure_installed!.

Ideally we'd bust all Tap class-level caches every time we add/remove a tap CC @reitermarkus