revert previous gdb.c commit (it was not a minor comment update)

gdb/ChangeLog:

       * gdb.c: Revert the previous change, which was probably committed
        by accident.

gdb/gdb.c

@@ -20,21 +20,16 @@
 #include "main.h"
 #include "gdb_string.h"
 #include "interps.h"
-#include <mcheck.h>
 
 int
 main (int argc, char **argv)
 {
   struct captured_main_args args;
-  int ret;
 
-  mtrace ();
   memset (&args, 0, sizeof args);
   args.argc = argc;
   args.argv = argv;
   args.use_windows = 0;
   args.interpreter_p = INTERP_CONSOLE;
-  ret = gdb_main (&args);
-  muntrace();
-  return ret;
+  return gdb_main (&args);
 }