From #60113 (comment)

Following #97671 and https://flutter-review.googlesource.com/c/recipes/+/26040, FlutterMacOS.framework contains the lipo'd x64 and arm64 engine dylib, and two new gen_snapshot binaries are included with the engine artifacts as follows:

• bin/cache/artifacts/engine/darwin-x64/gen_snapshot_x64
• bin/cache/artifacts/engine/darwin-x64/gen_snapshot_arm64
• bin/cache/artifacts/engine/darwin-x64-profile/gen_snapshot_x64
• bin/cache/artifacts/engine/darwin-x64-profile/gen_snapshot_arm64
• bin/cache/artifacts/engine/darwin-x64-release/gen_snapshot_x64
• bin/cache/artifacts/engine/darwin-x64-release/gen_snapshot_arm64

The tool should switch to using those gen_snapshots, and then we can remove the gen_snapshot that's still there that doesn't have a suffix that specifies the architecture.

Additionally, remove arm64 EXCLUDED_ARCHS (see #72748) so the apps actually start getting built natively.

@zanderso @knopp