Revert "liblp: Reclaim wasted space from unaligned partitions."

When this patch landed, it was thought that over-allocating partitions
had no undesired side effects. However there are cases where it is now
causing problems. When flashing a GSI for VTS, the vbmeta is appended to
the end of the partition. If libfs_avb cannot find this vbmeta by
looking at the end of the partition, verification will fail. Similar use
cases with verifying other dynamic partitions are expected to be
problematic, so for now we revert to block-size alignment.

This reverts commit dccfdca1.

Bug: 125113249
Test: liblp_test gtest
Change-Id: Ibfd66734b63265e9fbb2ccf6b670c168c36190bc