Remove ENTER and GUARD_OBJ macro #594

Job	Run time
ruby-versions / Generate Ruby versions	5s
ubuntu-latest 2.7	1m 4s
ubuntu-latest 3.2	33s
ubuntu-latest 3.1	36s
ubuntu-latest 3.0	32s
ubuntu-latest 3.3	36s
macos-latest 3.1	29s
ubuntu-latest 3.4	32s
macos-latest 3.3	32s
macos-latest 3.2	31s
macos-latest 3.0	26s
macos-latest debug	39s
macos-latest 3.4	23s
macos-latest 2.7	1m 1s
ubuntu-latest head	34s
ubuntu-latest debug	48s
macos-14 3.0	29s
macos-latest head	33s
macos-14 debug	40s
macos-14 2.7	1m 16s
macos-14 head	29s
macos-14 3.3	31s
macos-14 3.1	29s
windows-latest 2.7	3m 45s
windows-latest 3.4	2m 38s
windows-latest 3.3	2m 23s
windows-latest mswin	1m 26s
macos-14 3.4	32s
windows-latest mingw	2m 13s
windows-latest head	2m 14s
macos-14 3.2	30s
	29m 29s

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