Add `chomp` to `IO#readline` and `IO#readlines` #5466

Job	Run time
test (3.1, test)	2m 33s
test (3.2, test)	2m 21s
test (3.3, test)	2m 29s
test (head, test)	2m 5s
test (head, stdlib_test rubocop)	1m 46s
test (3.3, stdlib_test)	2m 12s
test (3.3, test, --enable-frozen-string-literal)	2m 32s
test (3.3, stdlib_test, --enable-frozen-string-literal)	2m 20s
test (3.3, lexer compile confirm_lexer)	3m 13s
test (3.3, rubocop validate test_doc build test_generate_stdlib raap)	2m 41s
test (3.3, typecheck_test)	1m 1s
	25m 13s

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