tap: revert caching Tap.reverse_tap_migrations_renames

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.

Library/Homebrew/tap.rb

@@ -820,7 +820,7 @@ class Tap
 
   sig { returns(T::Hash[String, T::Array[String]]) }
   def self.reverse_tap_migrations_renames
-    cache[:reverse_tap_migrations_renames] ||= Tap.each_with_object({}) do |tap, hash|
+    Tap.each_with_object({}) do |tap, hash|
       tap.tap_migrations.each do |old_name, new_name|
         new_tap_user, new_tap_repo, new_name = new_name.split("/", 3)
         next unless new_name