ptid_{lwp,tid}_p: Remove unnecessary checks

ptid_{lwp,tid}_p: Remove unnecessary checks

The calls to ptid_equal in ptid_lwp_p and ptid_tid_p that compare the
argument to minus_one_ptid and null_ptid are not necessary.  The calls
in question are:

   if (ptid_equal (minus_one_ptid, ptid)
       || ptid_equal (null_ptid, ptid))
     return 0;

minus_one_ptid is { .pid = -1, .lwp = 0, .tid = 0 }
null_ptid is { .pid = 0, .lwp = 0, .tid = 0 }

If the ptid argument is either of them, the statements

  return (ptid_get_lwp (ptid) != 0);

and

  return (ptid_get_tid (ptid) != 0);

will yield the same result (0/false).

gdb/ChangeLog:

	* common/ptid.c (ptid_lwp_p, ptid_tid_p): Remove comparison with
	minus_one_ptid and null_ptid.