remove _supported_fs v2

[Christoph Hellwig <hch@lst.de>]

Hi all,

this series removes the remaining _supported_fs calls and replaces them
with a new _exclude_fs call.

The first patch removes a _supported_fs for a relatively new test from
Brian that fails on other file systems.  We should still run it so that
people have a chance to fix the corruption, so I think this make sense.

Unlike the previous version this does not add a new ext-common directory,
but instead uses _exclude_fs for those tests as well, which doesn't
look quite as nice.  Some of the ext4 maintainers said they might want
to switch this to feature checks, which sounds great but also something
better done by people familiar with extN.

Changes since v1:
 - remove the separated ext-common directory previously added