block: remove BlockDriver.bdrv_write_compressed

block: remove BlockDriver.bdrv_write_compressed

There are no block drivers left that implement the old
.bdrv_write_compressed interface, so it can be removed. Also now we have
no need to use the bdrv_pwrite_compressed function and we can remove it
entirely.

Signed-off-by: Pavel Butsykin <[email protected]>
Reviewed-by: Stefan Hajnoczi <[email protected]>
Signed-off-by: Denis V. Lunev <[email protected]>
CC: Jeff Cody <[email protected]>
CC: Markus Armbruster <[email protected]>
CC: Eric Blake <[email protected]>
CC: John Snow <[email protected]>
CC: Stefan Hajnoczi <[email protected]>
CC: Kevin Wolf <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>