Don't redirect ldexp to scalbn in bits/math-finite.h (bug 19209).

bits/math-finite.h maps ldexp functions to corresponding scalbn
functions.  This is (a) a namespace bug for C90, which has ldexp but
not scalbn, and (b) in any case useless, since the ldexp and scalbn
functions have identical semantics (for floating-point types with
radix 2), and since the fix for bug 6803 are actually aliases
(presumably the mapping was based around the old bug of scalbn not
setting errno).  This patch removes the bogus redirections.

Tested for x86_64 and x86.

	[BZ #19209]
	* math/bits/math-finite.h (ldexp): Remove declaration.
	(ldexpf): Likewise.
	(ldexpl): Likewise.