Remove local copy of the flag file

This change removes the local copy of the flag file in PackageTable, and
FlagValueList.

PackageTable copied the entire flag file into memory, and the
FlagValueList copied the entire flag value list into memory. In this
change FlagValueList directly access the flag value list in the memory.
PackageTable will iterate the file, and find the target package node.

Change-Id: Id766c28b71a54290b266cc5f3f404f5c82590da2
Test: atest aconfig_storage_file.test.java aconfig_storage_read_api.test.java
Bug: 352078117