Remove the BFS spreading activation and MPFP (Multi-Path Fact Propagation)
graph retrieval strategies, leaving link_expansion as the sole graph
retrieval algorithm. Rename MPFPTimings to GraphRetrievalTimings and
mpfp_timings field to graph_timings since the timing struct is used by
LinkExpansionRetriever.
Deleted:
- hindsight-api-slim/hindsight_api/engine/search/mpfp_retrieval.py
- hindsight-api-slim/tests/test_mpfp_retrieval.py
Removed config: HINDSIGHT_API_MPFP_TOP_K_NEIGHBORS
ea834bc7dc