[State Sync Redesign 1.2] Delete dead EventEmitter events (`lock`, `unlock`)

`MetamaskController.emit('lock')` and `emit('unlock')` have zero listeners. Delete the emit calls.

## Steps

1. Delete `this.emit('lock')` call
2. Delete `this.emit('unlock')` call
3. Verify no listeners registered for either event

## Files

- `app/scripts/metamask-controller.js`

## Risk

None — dead code.

## Dependencies

None

## Context

Part of [State Sync Redesign — Epic 1: Transport optimization].

Start in app/scripts/metamask-controller.js and inspect the lock and unlock emit calls. Search the repository to verify that neither event has listeners, then confirm both calls are gone and the existing checks pass.

Written by the indexing model from the issue text.