Carrying on from commit 037cd0d991, removed the following unimplemented
instances of curlssl_close_all():
Curl_axtls_close_all()
Curl_darwinssl_close_all()
Curl_cyassl_close_all()
Curl_gskit_close_all()
Curl_gtls_close_all()
Curl_nss_close_all()
Curl_polarssl_close_all()
Perform more work in between sleeps. This is work around the
fact that axtls does not expose any knowledge about when work needs
to be performed. Depending on connection and how often perform is
being called this can save ~25% of time on SSL handshakes (measured
on 20ms latency connection calling perform roughly every 10ms).
