More memory-efficient packages state hash calculation.

Memory
Before: 7.24MB (https://pprof.corp.google.com/?id=41244f6c3fa65f54b930087939a28231&tab=bottomup&focus=computePackageStateHash)
After:  164KB (https://pprof.corp.google.com/?id=387efa039243c043f051f596dc4f3fd8&tab=bottomup&focus=computePackageStateHash)

Time
Before:
computePackageStateHashTime for user [0]: 2196mcs, packages: 286
computePackageStateHashTime for user [0]: 2077mcs, packages: 286
computePackageStateHashTime for user [0]: 9854mcs, packages: 286
computePackageStateHashTime for user [0]: 7619mcs, packages: 286
computePackageStateHashTime for user [0]: 6518mcs, packages: 286

After:
computePackageStateHashTime for user [0]: 2766mcs, packages: 286
computePackageStateHashTime for user [0]: 2999mcs, packages: 286
computePackageStateHashTime for user [0]: 2489mcs, packages: 286
computePackageStateHashTime for user [0]: 6040mcs, packages: 286
computePackageStateHashTime for user [0]: 4562mcs, packages: 286

Bug: 195992187
Test: heap profile during reboot and install/uninstall
Change-Id: Id77fe423c6a12404119af838e05ed5d7565591be