ext4: remove checks for e_value_block

Currently we don't support xattrs with e_value_block set. We don't allow
them to pass initial xattr check so there's no point for checking for
this later. Since these tests were untested, bugs were creeping in and
not all places which should have checked were checking e_value_block
anyway.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>