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.

package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "xterm",
-  "version": "3.1.0-master",
+  "version": "3.2.0",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {