common: Use _require_xfs_io_command() instead of helpers

common: Use _require_xfs_io_command() instead of helpers

Number of helpers for checking xfs_io functionality is slowly
growing.  But it's as easy to simply use _require_xfs_io_command()
directly and just specify the command we want to check. It will also
avoid the need to create helper every time we need to check a new
command in xfs_io.

Remove all the helpers and use _require_xfs_io_command() in the
tests.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>