[llvm] [orc] Reduce memory usage from empty materialization info DenseMaps (PR #88167)

[Ben Langmuir via llvm-commits]

benlangmuir wrote:

@lhames I added these calls after every loop that calls `erase()` on the materialization infos; if there's a more central place I could put this please let me know, but I didn't see an obvious candidate.

https://github.com/llvm/llvm-project/pull/88167