RFC: remove CONFIG_EXT4_FS_XATTR

[Theodore Ts'o <tytso@mit.edu>]

The number of build warnings that were generated with the inline data
patch makes me think that perhaps we should just remove
CONFIG_EXT4_FS_XATTR.  Turning off CONFIG_EXT4_FS_XATTR causes a net
decrease in the ext4 file system by 27k (about 7.3% if ext4 is built as
a module; the entire compiled kernel's text+data size for my
all-in-one-no-modules-for-kvm-testing is 19 megabytes).

Another advantage of making this change is with the inline data option,
if you turn off CONFIG_EXT4_FS_XATTR, it will still allow a file system
with inline_data to be mounted, but then attempts to read small files or
small directories will end up returning EOPNOTSUPP, which will be
surprising to end users in a very serious way.  (Assuming it works at
all; I haven't tested to make sure it fails cleanly, and I'm not sure
Tao has tested that case either; so easing our test matrix is another
reason why removing this config option would be helpful.)

Does anyone have any objections or other reasons why this would be a bad
idea?

                                                - Ted