Assume __NR_utimensat is always defined

With the 2.6.32 minimum kernel on x86 and 3.2 on other architectures,
__NR_utimensat is always defined.

Changelog:
	* sysdeps/unix/sysv/linux/futimens.c (futimens) [__NR_utimensat]:
	Make code unconditional.
	[!__NR_utimensat]: Remove conditional code.
	* sysdeps/unix/sysv/linux/lutimes.c (lutimes) [__NR_utimensat]:
	Make code unconditional.
	[!__NR_utimensat]: Remove conditional code.
	* sysdeps/unix/sysv/linux/utimensat.c (utimensat) [__NR_utimensat]:
	Make code unconditional.
	[!__NR_utimensat]: Remove conditional code.