Phase 1: Stop compiling "acting as a directory cache" in --disable-module-relay
We want to stop compiling the code that makes tor act as a directory cache, when the relay module is disabled.
(We already disable DirPort and DirCache, so the functionality is not available.)
At each stage, we should work to minimize layer-violations: there should generally not be calls from src/core/ into relay-specific code, and we should plan to refactor as needed to minimize them. We can reduce layer violations in parallel with the above.