Add noUnusedLocals tsconfig flag, fix issues

Two parts were commented out:
- _writeStopped: This is because _xoffSentToCatchUp references this variable
  and the feature is sort of half implemented/disabled.
- _clearChar: This is because some comments still reference this, it's part
  of the work needed to do better line redrawing.

src/utils/CircularList.test.ts

@@ -6,10 +6,6 @@
 import { assert } from 'chai';
 import { CircularList } from './CircularList';
 
-class TestCircularList<T> extends CircularList<T> {
-  public get array(): T[] { return this._array; }
-}
-
 describe('CircularList', () => {
   describe('push', () => {
     it('should push values onto the array', () => {