Remove unused sparc64/soft-fp libm function implementations.

sysdeps/sparc/sparc64/soft-fp has files s_frexpl.c, s_scalblnl.c and
s_scalbnl.c that are never used because the ldbl-128 versions always
come first in the sysdeps directory ordering.  This patch removes the
unused files.

Tested with build-many-glibcs.py that installed stripped shared
libraries are unchanged by this patch.

	* sysdeps/sparc/sparc64/soft-fp/s_frexpl.c: Remove file.
	* sysdeps/sparc/sparc64/soft-fp/s_scalblnl.c: Likewise.
	* sysdeps/sparc/sparc64/soft-fp/s_scalbnl.c: Likewise.