struct Curl_share: provide sslsession unconditionally

It makes much nicer and less convuluted code everywhere if this struct
member is always present even when libcurl is built without SSL support.

This reverts parts of commit 15e3e451

lib/share.h

@@ -50,9 +50,7 @@ struct Curl_share {
   struct CookieInfo *cookies;
 #endif
 
-#ifdef USE_SSL
   struct curl_ssl_session *sslsession;
-#endif
   unsigned int nsslsession;
 };