drop the medium DiT .xnnwc weight caches (regenerated locally)

Not in the install manifest (never auto-downloaded); the runtime rebuilds the cache locally on first run (weight_cache_path=auto). Measured benefit of a shipped cache is only ~2.4s (construct) — per-rung time is forward compute, unaffected. Removes ~7 GB of dead weight, and a locally-built cache is safer (a cache built on one CPU may not load on another). Matches the small DiTs, which ship no .xnnwc.

tflite/sa3-m/dit_fp32.tflite.xnnwc

@@ -1,3 +0,0 @@
-version https://git-lfs.github.com/spec/v1
-oid sha256:7cd74a23f88a21e40496b9cdd1ee8f1c4af71da0cb49a8173084cb2109f3bf39
-size 5722246888

tflite/sa3-m/dit_w8a8.tflite.xnnwc

@@ -1,3 +0,0 @@
-version https://git-lfs.github.com/spec/v1
-oid sha256:11948de1ab974e009587704d3b816ea56039fe3cd7f9c9342eda6b1307cd9d84
-size 1440076384