On most platforms, we support only a single host architecture and a single target architecture per build. macOS supports both arm64 and x86_64 host platforms via multi-arch (universal) binaries generated with the lipo tool and as such, we have two gen_snapshot binaries, one for each target architecture. These binaries are universal binaries named gen_snapshot_${target_arch}. The unqualified gen_snapshot binary used for other platforms is unused on macOS and we should eliminate it from the cache, and update all references in the tool.

Related issues:

• Build macOS desktop gen_snapshot_arm64 and gen_snapshot_x64 as arm64 binary to run natively on Apple Silicon #101138
• Build Flutter macOS artifacts with ARM architecture slice #69157

Previous attempt at this PR:

• [macOS] Only bundle gen_snapshot_${target_arch} engine#53971