Do not typedef ExtensionId/ID, since it's already available in extension_id.h

BUG=None
Test=None, minor cleanup.

Review-Url: https://codereview.chromium.org/2494113003
Cr-Commit-Position: refs/heads/master@{#431738}
10 files changed