revert(perf): remove Flerovium and the spawn tuning

Run 3 benches (analysis/client-perf/RESULTS-proxy.md): Flerovium's run-2
win did not reproduce (S1 slightly worse, S3 within noise), and the
moderate spawn tuning (d80f85b, 8e8483d) left total mob counts unchanged
across 4 runs per config. Owner approved removing both. The mods now
regenerate their default spawn configs.

pack.toml

@@ -6,7 +6,7 @@ pack-format = "packwiz:1.1.0"
 [index]
 file = "index.toml"
 hash-format = "sha256"
-hash = "1ec4be75b6fe3d25a6d80d8274baea07b9b0f84300a56a8d101108980199f05e"
+hash = "07463f2d8920a7a3ec3f9b3d7d5f0883ed265d3bc8c34e0c956b09d8ce277814"
 
 [versions]
 minecraft = "1.21.1"