Do not check for ERR_remove_thread_state() (do not link ssl into every library)

Do not check for ERR_remove_thread_state() (do not link ssl into every library)

This reverts commit c4e9d9bd662de7f575f2172c160795d452ebe709
("sample/https-client: check for ERR_remove_thread_state() existence").

Calling AC_SEARCH_LIBS() modifies LIBS - -lcrypto incorrectly
ends up in LIBS, and thus linked to by libevent_core.so.

Checking for ERR_remove_thread_state should no longer be needed
because it was introduced in openssl 1.0.0, and the previous line
0.9.8 had support discontinued at the end of 2015.

Fixes: #473