Delete 68 files: replace centres CIP library with CDK native stereo

Rewrote StereoCenteralityTool to use CDK 2.12's built-in
IStereoElement (ITetrahedralChirality, IDoubleBondStereochemistry)
instead of the custom 60-file centres CIP priority library.

Deleted:
- Entire centres/ package (60 files, ~4000 lines)
- 3 unused fingerprint interfaces (IDataStore, IWalker, ISPWalker)
- 5 orphan files from previous commits

345 → 277 Java files (20% reduction). All 135 tests pass.
Test suite 20% faster (103s → 83s) due to CDK native stereo.

Co-Authored-By: Syed Asad Rahman <asad.rahman@bioinceptionlabs.com>

Author: asad