libssh: remove CURLOPT_SSL_VERIFYHOST check

It was never meant for SSH: it should rely on the knownhosts file (if
set) in the same way libssh2 already does.

Reported-by: James Abbatiello
Fixes #13767
Closes #13781

lib/vssh/libssh.c

@@ -388,10 +388,7 @@ static int myssh_is_known(struct Curl_easy *data)
     goto cleanup;
   }
 
-  if(data->set.ssl.primary.verifyhost != TRUE) {
-    rc = SSH_OK;
-    goto cleanup;
-  }
+  if(data->set.str[STRING_SSH_KNOWNHOSTS]) {
 
 #if LIBSSH_VERSION_INT >= SSH_VERSION_INT(0,9,0)
     /* Get the known_key from the known hosts file */
@@ -533,6 +530,7 @@ static int myssh_is_known(struct Curl_easy *data)
         goto cleanup;
       }
     }
+  }
   rc = SSH_OK;
 
 cleanup: