chore: cleanup vestigial old architecture java remnants

[mikehardy]

Summary

• Deletes six unregistered legacy Android bridge modules (ReactNativeFirebase*Module.java in app/utils, app, remote-config, perf, in-app-messaging, installations) left behind after the TurboModule migration. Runtime was already TurboModule-only; these classes were compiled but never registered, so they were unreachable.
• Quick coverage win: Jacoco overall LINE coverage rises from 10.75% → 11.19% (+0.44 pp) by removing 430 impossible-to-cover lines (all 0% at baseline).
• Updates the OKF “Dead legacy shells” gotcha to past tense so it no longer links at a deleted file.

Test plan

• Area-focused e2e (app, remoteConfig, perf, inAppMessaging, installations): Android 141 passing, iOS 141 passing, macOS 66 passing
• yarn lint exit 0 on frozen tree
• Jacoco post-e2e before/after confirms missed LINE −430 and overall 10.75% → 11.19%

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.82%. Comparing base (3bbfecc) to head (2939ee4).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #9109      +/-   ##
============================================
+ Coverage     65.14%   65.82%   +0.69%     
+ Complexity     1833     1832       -1     
============================================
  Files           503      497       -6     
  Lines         39184    38754     -430     
  Branches       5805     5785      -20     
============================================
- Hits          25521    25506      -15     
+ Misses        12192    11813     -379     
+ Partials       1471     1435      -36     

Flag	Coverage Δ
android-native	62.98% <ø> (+2.46%)	⬆️
e2e-ts-android	59.69% <ø> (+1.49%)	⬆️
e2e-ts-ios	62.75% <ø> (-0.05%)	⬇️
e2e-ts-macos	50.01% <ø> (ø)
ios-native	62.75% <ø> (-0.05%)	⬇️
jest	49.58% <ø> (ø)

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[mikehardy]

Going to merge this one as there is literally no code to review, it's all deletions of stale files I missed during new arch migraiton:

• feat!: migrate to TurboModules #9080

Additionally, since there is a new PR that touches one of these files I was surprised to see laying around I want to get this in now so the new PR may be updated to reflect the new arch reality:

• fix(app, android): run makeGooglePlayServicesAvailable on the main thread #9107