Fix: Make `Crystal::EventLoop#remove(io)` a class method #13056

Job	Run time
check_format	1m 35s
x86_64-gnu-test-preview_mt	5m 50s
x86_64-musl-test	37m 57s
x86_64-gnu-test (1.7.3)	35m 13s
x86_64-gnu-test (1.8.2)	34m 37s
x86_64-gnu-test (1.9.2)	34m 23s
x86_64-gnu-test (1.10.1)	33m 24s
x86_64-gnu-test (1.11.2)	33m 11s
x86_64-gnu-test (1.12.2)	36m 8s
x86_64-gnu-test (1.13.3)	32m 17s
x86_64-gnu-test (1.14.0)	32m 29s
x86_64-gnu-test (1.0.0, FLAGS=-Dwithout_ffi USE_PCRE1=true)	31m 54s
x86_64-gnu-test (1.1.1, FLAGS=-Dwithout_ffi USE_PCRE1=true)	32m 35s
x86_64-gnu-test (1.2.2, USE_PCRE1=true)	34m 0s
x86_64-gnu-test (1.3.2, USE_PCRE1=true)	37m 38s
x86_64-gnu-test (1.4.1, USE_PCRE1=true)	33m 34s
x86_64-gnu-test (1.5.1, USE_PCRE1=true)	32m 10s
x86_64-gnu-test (1.6.2, USE_PCRE1=true)	34m 8s
	9h 13m 3s

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