[NFC] MemoryDependenceAnalysis cleanup.

1. Removed redundant includes,
2. Removed never defined and used `releaseMemory()`.
3. Fixed member functions names first letter case.
4. Renamed duplicate (in nested struct `NonLocalPointerInfo`) name
   `NonLocalDeps` to `NonLocalDepsMap`.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D102358