block.h: remove outdated comment

The comment "disk I/O throttling" doesn't make any sense at all
any more. It was added in commit 0563e19 to describe
bdrv_io_limits_enable()/disable(), which were removed in commit
9714807, so the comment is just a forgotten leftover.

Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Message-Id: <20220131125615.74612-1-eesposit@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

include/block/block.h

@@ -344,7 +344,6 @@ typedef unsigned int BdrvChildRole;
 char *bdrv_perm_names(uint64_t perm);
 uint64_t bdrv_qapi_perm_to_blk_perm(BlockPermission qapi_perm);
 
-/* disk I/O throttling */
 void bdrv_init(void);
 void bdrv_init_with_whitelist(void);
 bool bdrv_uses_whitelist(void);