ext4: Remove CONFIG_EXT4_FS_XATTR

Ted has sent out a RFC about removing this feature. Eric and Jan
confirmed that both RedHat and SUSE enable this feature in all their
product.  David also said that "As far as I know, it's enabled in all
Android kernels that use ext4."  So it seems OK for us.

And what's more, as inline data depends its implementation on xattr,
and to be frank, I don't run any test again inline data enabled while
xattr disabled.  So I think we should add inline data and remove this
config option in the same release.

[ The savings if you disable CONFIG_EXT4_FS_XATTR is only 27k, which
  isn't much in the grand scheme of things.  Since no one seems to be
  testing this configuration except for some automated compile farms, on
  balance we are better removing this config option, and so that it is
  effectively always enabled. -- tytso ]

Cc: David Brown <davidb@codeaurora.org>
Cc: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Tao Ma <boyu.mt@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

Documentation/filesystems/ext4.txt

@@ -200,12 +200,9 @@ inode_readahead_blks=n	This tuning parameter controls the maximum
 			table readahead algorithm will pre-read into
 			the buffer cache.  The default value is 32 blocks.
 
-nouser_xattr		Disables Extended User Attributes. If you have extended
-			attribute support enabled in the kernel configuration
-			(CONFIG_EXT4_FS_XATTR), extended attribute support
-			is enabled by default on mount. See the attr(5) manual
-			page and http://acl.bestbits.at/ for more information
-			about extended attributes.
+nouser_xattr		Disables Extended User Attributes.  See the
+			attr(5) manual page and http://acl.bestbits.at/
+			for more information about extended attributes.
 
 noacl			This option disables POSIX Access Control List
 			support. If ACL support is enabled in the kernel