prune obsolete #include

hmac.h was needed only for the cram-md5 implementation.

src/socket.c

@@ -39,7 +39,6 @@
 #ifdef HAVE_LIBSSL
 # include <openssl/ssl.h>
 # include <openssl/err.h>
-# include <openssl/hmac.h>
 # include <openssl/x509v3.h>
 #endif