Remove broken CI cache

[paulb777]

Fix #12596

Remove the broken and deprecated cache from CI.

All cache actions have started to fail in the last day with:

Run mikehardy/buildcache-action@c87cea0ccd718971d6cc39e672c4f26815b6c126
buildcache: release file based on runner os is buildcache-macos.zip
Error: buildcache: failure during restore: HttpError: Not Found
Error: HttpError: Not Found

I also noticed that many of our cache usages (like on pod lib lint commands) were no-ops since the cache was only actually set up via build.sh and a few other scripts.

[google-oss-bot]

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Test Logs

• Base (9b661b0): https://github.com/firebase/firebase-ios-sdk/actions/runs/8397008356
• Merge (a43b9ec): https://github.com/firebase/firebase-ios-sdk/actions/runs/8402380990

1. https://storage.googleapis.com/firebase-sdk-metric-reports/KYDDf6JNVC.html

[paulb777]

After two days of failures, the cache started working again.

This will need to be revisited but can wait for now.