speed: Drop code to handle platforms without SIGALRM
speed: Drop code to handle platforms without SIGALRM

(except for Windows where a separate thread stops the looping)

Reviewed-by: Paul Dale <ddec78389666b4f7c9b4d110380c848489a3e4aa@openssl.org>
Reviewed-by: Richard Levitte <5fb523282dd7956571c80524edc2dccfa0bd8234@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14228)

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl