fsck.ubifs: rebuild_fs: Remove deleted nodes from valid node tree

fsck.ubifs: rebuild_fs: Remove deleted nodes from valid node tree

This is the 2/12 step of rebuilding. Traverse nodes from del_inos and
del_dents trees, remove inode nodes and dentry nodes with smaller sqnum
from valid trees.

This step handles deleting case, for example, file A is deleted, deleted
inode node and deleted dentry node are written, if we ignore the deleted
nodes, file A can be recovered after rebuilding because undeleted inode
node and undeleted dentry node can be scanned. There's an exception, if
deleted inode node and deleted dentry node are reclaimed(by gc) after
deletion, file A is recovered. UBIFS rebuild_fs cannot solve it, because
the real existence information of nodes depends on TNC, but TNC should
not be depended for UBIFS rebuild_fs.

Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>