Remove an unnecessary block in call_function_by_hand_dummy

Remove an unnecessary block in call_function_by_hand_dummy

I noticed that call_function_by_hand_dummy has a block that only
exists to declare a variable, like:

    {
      int i;
      for (i = ...0)
	...
    }

This patch removes the unnecessary and the extra indentation by moving
the declaration into the "for".

gdb/ChangeLog
2018-09-14  Tom Tromey  <tom@tromey.com>

	* infcall.c (call_function_by_hand_dummy): Remove unnecessary
	block.