Release bitmap object after task snapshot restore from disk.

So that the corresponding bitmap resource can be released earlier.

Flag: EXEMPT bugfix
Bug: 238206323
Test: Verify no AHardwareBuffer remains in the system server after
loading any snapshot from disk; this can be done by checking
dmabuf_dump after boot up & unlock device.

Change-Id: I3eda4dfe4fb6e9669cfc0e05f2ae85c904783af9