Revamp vdex format for better extensibility.

- Remove class loader context and boot classpath checksum sections.
  Those are not needed now that VerifierDeps don't depend on them.
- Remove remaining quickening encoding.
- Introduce sections in a vdex file, which can be extended without
  requiring a version change.

Test: test.py
Bug: 160294863

Change-Id: I4e3e25f34d242dc4de37f30ba9d78bcffbc1436d
13 files changed