ext4: don't show usrquota/grpquota twice in /proc/mounts

We now print mount options in a generic fashion in
ext4_show_options(), so we shouldn't be explicitly printing the
{usr,grp}quota options in ext4_show_quota_options().

Without this patch, /proc/mounts can look like this:

 /dev/vdb /vdb ext4 rw,relatime,quota,usrquota,data=ordered,usrquota 0 0
                                      ^^^^^^^^              ^^^^^^^^

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org