AOSP: e2fsdroid: Properly free the dedup block map.

AOSP: e2fsdroid: Properly free the dedup block map.

When BaseFS specifies the same block for two files, it gets added to a
separate "dedup" bitmap, and removed from the free block bitmap. If the
new build does not use every block in this bitmap, there will be an
inconsistency: the block bitmap marks blocks as in-use when they are
actually free. Although this doesn't matter for AOSP's read-only file
systems, it does cause e2fsck to complain, which breaks the build.

Fix the inconsistency by properly freeing all unused blocks within the
dedup block set.

Bug: 139201772
Test: build AOSP using BaseFS
Change-Id: I6b6511eb713a56fec932f1d5668f1766d64d9479
From AOSP commit: 346bee6f8b97aefe7714688f738606c116099fbc