fastbootd: Cancel snapshots when modifying partitions.

When flashing or resizing partitions, remove the
LP_PARTITION_ATTR_UPDATED flag. This will cause first-stage init to skip
any snapshots for that partition, and the backing storage (if any)
will later be reclaimed.

Bug: 139155473
Test: manual test
Change-Id: I3b185f68dfecb5a93636af0b5ae289ead1363fd0