ext2: remove duplicate 'ext2_get_acl()' define

When commit 4e34e719

 ("fs: take the ACL checks to common code")
changed the xyz_check_acl() functions into the more natural
xyz_get_acl() interface, we grew two copies of the

  #define ext2_get_acl	NULL

define for the non-acl case.

Remove the extra one.

Reported-by: Marco Stornelli <marco.stornelli@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>