Remove __ASSUME_AT_RANDOM.

This patch removes __ASSUME_AT_RANDOM now it can be assumed to be true
unconditionally.

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

	* sysdeps/unix/sysv/linux/kernel-features.h (__ASSUME_AT_RANDOM):
	Remove macro.
	* sysdeps/unix/sysv/linux/dl-osinfo.h (_dl_setup_stack_chk_guard)
	[!__ASSUME_AT_RANDOM]: Remove conditional code.
	(_dl_setup_pointer_guard) [!__ASSUME_AT_RANDOM]: Likewise.