xfs: don't allow disabling quota accounting on a mounted file system

Hi all,

disabling quota accounting (vs just enforcement) on a running file system
is a fundamentally race and hard to get right operation.  It also has
very little practical use.

Note that the quotaitem log recovery code is left for to make sure we
don't introduce inconsistent recovery states.

A series has been sent to make xfstests cope with this feature removal.

Changes since v1:
 - fix a spelling mistake

v2.1: [djwong] add patch to remove xfs_dqrele_all_inodes
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