ubifs: remove obsolete CONFIG_UBIFS_FS_XATTR symbol

550-ubifs-symlink-xattr-support.patch contains a reference to the
by now obsolete config symbol CONFIG_UBIFS_FS_XATTR which leads to
the functionality originally added by the patch in r30794 being
left-out during compile since commit 1bdcc63112a0
("UBIFS: remove xattr Kconnfig option") in v3.5.
Fix this by removing the #ifdef from all affected kernels as XATTR
support is now always enabled for UBIFS as well.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@40864 3c298f89-4303-0410-b956-a3cf2f4a3e73