Revert "alias_method is private on Ruby 2.3 and 2.4" #153

Job	Run time
ruby-versions / Generate Ruby versions	2s
ubuntu-20.04 2.5	1m 17s
ubuntu-20.04 2.6	1m 39s
ubuntu-20.04 2.7	1m 33s
ubuntu-20.04 3.0	39s
ubuntu-20.04 3.1	34s
ubuntu-20.04 3.2	26s
ubuntu-20.04 head	37s
ubuntu-20.04 jruby	1m 29s
ubuntu-20.04 jruby-head	2m 12s
ubuntu-20.04 truffleruby	55s
ubuntu-20.04 truffleruby-head	1m 29s
ubuntu-22.04 2.5	1m 25s
ubuntu-22.04 2.6	1m 13s
ubuntu-22.04 2.7	1m 11s
ubuntu-22.04 3.0	2m 0s
ubuntu-22.04 3.1	40s
ubuntu-22.04 3.2	28s
ubuntu-22.04 head	28s
ubuntu-22.04 jruby	1m 29s
ubuntu-22.04 jruby-head	1m 38s
ubuntu-22.04 truffleruby	1m 7s
ubuntu-22.04 truffleruby-head	58s
macos-11 2.5	2m 8s
macos-11 2.6	2m 39s
macos-11 2.7	2m 16s
macos-11 3.0	41s
macos-11 3.1	38s
macos-11 3.2	42s
macos-11 head	41s
macos-11 jruby	1m 24s
macos-11 jruby-head	1m 40s
macos-11 truffleruby	1m 17s
macos-11 truffleruby-head	1m 35s
macos-12 2.5	3m 6s
macos-12 2.6	3m 14s
macos-12 2.7	2m 32s
macos-12 3.0	50s
macos-12 3.1	44s
macos-12 3.2	55s
macos-12 head	54s
macos-12 jruby	1m 28s
macos-12 jruby-head	2m 21s
macos-12 truffleruby	1m 22s
macos-12 truffleruby-head	1m 24s
windows-latest 2.5	9m 4s
windows-latest 2.6	2m 58s
windows-latest 2.7	3m 2s
windows-latest 3.0	2m 26s
windows-latest 3.1	1m 21s
windows-latest 3.2	2m 38s
windows-latest head	1m 44s
ubuntu-latest jruby-9.2	2m 9s
ubuntu-latest jruby-9.3	1m 28s
	1h 26m 50s

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