Remove __ASSUME_XFS_RESTRICTED_CHOWN.

Remove __ASSUME_XFS_RESTRICTED_CHOWN.

This patch removes the __ASSUME_XFS_RESTRICTED_CHOWN macro, now it can
be presumed to be defined unconditionally.  I'm not sure if what's
left of __statfs_chown_restricted is actually useful (if not, a
followup could remove it), but I left it there to keep the patch
conservative and avoid changing the code generated for glibc.

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

	* sysdeps/unix/sysv/linux/kernel-features.h
	(__ASSUME_XFS_RESTRICTED_CHOWN): Remove macro.
	* sysdeps/unix/sysv/linux/pathconf.c (__statfs_chown_restricted)
	[__ASSUME_XFS_RESTRICTED_CHOWN]: Make code unconditional.
	(__statfs_chown_restricted) [!__ASSUME_XFS_RESTRICTED_CHOWN]:
	Remove conditional code.