fix(android): revert resolveReactHost logic to use getReactHost()

[floydkim]

Background

Our support policy is:

• RN 0.76 and below should use react-native-code-push@12.0.2
• This library supports RN 0.77+ only

In a recent commit, resolveReactHost in CodePushNativeModule.java became overly complex to preserve legacy compatibility.
Given the current support range, that reflection-based path is no longer needed.

What changed

1) Reverted recent changes to simplify resolveReactHost (Android)

• Resolve ReactDelegate
• Return reactDelegate.getReactHost() directly

2) Removed RN <=0.76 from E2E matrix

• Updated RN CLI E2E matrix targets to start from RN 0.77.x

Why:

• RN <=0.76 is intentionally frozen at 12.0.2
• Keeping those versions in this repo’s active E2E matrix creates noise and implies support outside current policy
• Matrix coverage should reflect the actual maintained support range (0.77+)

Why this is needed

• Align implementation and test coverage with the official support policy
• Reduce maintenance overhead from unnecessary legacy branches
• Keep CI/E2E signal focused on actively supported RN versions

Validation

• local E2E passed
  • RN 0.77 ~ 0.84 (New and Legacy Architecture both)
  • Expo 54, 55 Beta