Clean up ldbl-128 / ldbl-128ibm expm1l dead code (bug 16415).

Clean up ldbl-128 / ldbl-128ibm expm1l dead code (bug 16415).

The ldbl-128 and ldbl-128ibm expm1l implementations have code to
handle +Inf and finite arguments above an overflow threshold.  Since
they now use __expl for large positive arguments to fix other
problems, this code is unreachable; this patch removes it.

Tested for mips64 and powerpc.

	[BZ #16415]
	* sysdeps/ieee754/ldbl-128/s_expm1l.c (maxlog): Remove variable.
	(__expm1l): Remove code to handle positive infinity and overflow.
	* sysdeps/ieee754/ldbl-128ibm/s_expm1l.c (maxlog): Remove
	variable.
	(__expm1l): Remove code to handle positive infinity and overflow.