Remove __ASSUME_UTIMENSAT.

Remove __ASSUME_UTIMENSAT.

This patch removes the __ASSUME_UTIMENSAT macro, now it can be
unconditionally assumed to be true.

This shows that the only live uses of __ASSUME_UTIMES are in utimes.c
and they are only live for hppa.  I intend a followup patch to make
__ASSUME_UTIMES into an hppa-specific macro (not used or defined
outside sysdeps/unix/sysv/linux/hppa/).

Tested x86_64 that the disassembly of installed shared libraries is
unchanged by this patch.

	* sysdeps/unix/sysv/linux/kernel-features.h (__ASSUME_UTIMENSAT):
	Remove macro.
	* sysdeps/unix/sysv/linux/futimes.c: Do not include
	<kernel-features.h>.
	[__NR_utimensat && !__ASSUME_UTIMENSAT] (miss_utimensat): Remove
	conditional variable definition.
	(__futimes): Update comment.
	(__futimes) [__ASSUME_UTIMENSAT]: Make code unconditional.
	(__futimes) [!__ASSUME_UTIMENSAT]: Remove conditional code.