iomap: Remove large folio handling in iomap_invalidate_folio()

We do not need to release the iomap_page in iomap_invalidate_folio()
to allow the folio to be split.  The splitting code will call
->release_folio() if there is still per-fs private data attached to
the folio.  At that point, we will check if the folio is still dirty
and decline to release the iomap_page.  It is possible to trigger the
warning in perfectly legitimate circumstances (eg if a disk read fails,
we do a partial write to the folio, then we truncate the folio), which
will cause those writes to be lost.

Fixes: 60d82310 ("iomap: Support large folios in invalidatepage")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>