Refactor RAND_set_entropy_source #1377

Job	Run time
basic_clang	4m 29s
basic_gcc	4m 21s
check_update	59s
check-ansi	1m 59s
minimal	2m 26s
no-deprecated	4m 9s
address_ub_sanitizer	11m 10s
buildtest	7m 18s
enable_non-default_options	3m 38s
fips_and_ktls	4m 25s
legacy	3m 38s
memory_sanitizer	26m 58s
no-legacy	4m 27s
non-caching	4m 25s
no-shared (ubuntu-latest)	3m 18s
ntls_address_ub_sanitizer	9m 42s
ntls_memory_sanitizer	17m 34s
no-shared (macos-latest)	3m 46s
symbol_prefix-test	7m 13s
threads_sanitizer	3m 33s
EC_POINTs_api_test	19m 7s
external-test-pyca (1.51.0, 3.9)	1m 26s
ntls-with-fips	8m 10s
ntls-without-sm234	6m 48s
out-of-source-and-install (ubuntu-latest)	4m 20s
out-of-source-and-install (macos-latest)	3m 24s
phe_test	35m 0s
sm2-threshold-test	44m 5s
smtc_and_ntls	2m 8s
zkp-build-test	3m 18s
	4h 17m 14s

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