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/InputHandler.ts

@@ -4,7 +4,7 @@
  * @license MIT
  */
 
-import { CharData, IInputHandler, IInputHandlingTerminal, ITerminal } from './Types';
+import { CharData, IInputHandler, IInputHandlingTerminal } from './Types';
 import { C0 } from './EscapeSequences';
 import { DEFAULT_CHARSET } from './Charsets';
 import { CHAR_DATA_CHAR_INDEX, CHAR_DATA_WIDTH_INDEX } from './Buffer';