writeback: remove inode_to_wb_is_valid()

inode_to_wb_is_valid() is no longer used since commit fe55d563
("remove inode_congested()"), remove it.

Link: https://lkml.kernel.org/r/20220714084147.140324-1-xiujianfeng@huawei.comSigned-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/backing-dev.h

@@ -229,18 +229,6 @@ wb_get_create_current(struct backing_dev_info *bdi, gfp_t gfp)
 	return wb;
 }
 
-/**
- * inode_to_wb_is_valid - test whether an inode has a wb associated
- * @inode: inode of interest
- *
- * Returns %true if @inode has a wb associated.  May be called without any
- * locking.
- */
-static inline bool inode_to_wb_is_valid(struct inode *inode)
-{
-	return inode->i_wb;
-}
-
 /**
  * inode_to_wb - determine the wb of an inode
  * @inode: inode of interest
@@ -339,11 +327,6 @@ wb_get_create_current(struct backing_dev_info *bdi, gfp_t gfp)
 	return &bdi->wb;
 }
 
-static inline bool inode_to_wb_is_valid(struct inode *inode)
-{
-	return true;
-}
-
 static inline struct bdi_writeback *inode_to_wb(struct inode *inode)
 {
 	return &inode_to_bdi(inode)->wb;