Simplify the command factory

Since more than an year it not possible to create commands in the heap
but they are allocated on the stack and directly run. In this regard, it
doesn't make sense to have all the vararg stuff. Commands made sense
to be created and pushed onto a stack then a general executor will
run thru the stack and execute/handle the commands.

Author: faizshukri

ext/mysqlnd/mysqlnd_auth.c

@@ -196,7 +196,7 @@ mysqlnd_switch_to_ssl_if_needed(MYSQLND_CONN_DATA * const conn,
 
 	{
 		const size_t client_capabilities = mysql_flags;
-		ret = conn->run_command(COM_ENABLE_SSL, conn, client_capabilities, server_capabilities, charset_no);
+		ret = conn->command->enable_ssl(conn, client_capabilities, server_capabilities, charset_no);
 	}
 	DBG_RETURN(ret);
 }