[compiler] Remove unused collections in HIR passes (#37699)

## Summary

Remove two collections that are populated but never read during React
Compiler passes:

- `terminalPreds` in `propagateNonNull`
- `placeScopes` in `alignReactiveScopesToBlockScopesHIR`

This avoids allocating and updating unused state while leaving the
passes' outputs unchanged.

Supersedes #37698, which was opened from the wrong GitHub account.

## How did you test this change?

- `env -u FORCE_COLOR -u NO_COLOR yarn workspace
babel-plugin-react-compiler test` — 1,827 tests passed.
- Prettier check passed for both changed files.

Co-authored-by: irontaek <13810291+irontaek@users.noreply.github.com>