Remove __libc_nanosleep function name.

Continuing the removal of unused __libc_* function names, this patch
removes the __libc_nanosleep name.

Tested for x86_64 (testsuite, and that the disassembly of installed
shared libraries is unchanged by the patch; __nanosleep changes from
weak to strong, which is of no significance).

	* posix/nanosleep.c (__libc_nanosleep): Rename to __nanosleep.
	(__nanosleep): Do not define as alias.
	(nanosleep): Define as alias of __nanosleep.
	* sysdeps/unix/sysv/linux/syscalls.list (nanosleep): Remove
	__libc_nanosleep name.