fs: remove emergency_thaw_bdev

Fold emergency_thaw_bdev into it's only caller, to prepare for buffer.c
to be built only when buffer_head support is enabled.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Link: https://lore.kernel.org/r/20230801172201.1923299-2-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>