Remove tsc-watch dependency which is no longer used.

It appears that the original necessity for `tsc-watch` was introduced
through new usage within `npm-scripts` commands in
#632.

Since that usage is no longer present (at least partially removed via
5f287d9), this dependency should no longer
be necessary either.

This is relatively urgent since `tsc-watch` includes the `event-stream` npm
package as a transitive dependency and that package is demonstrably
vulnerable:

Ref: dominictarr/event-stream#116

cc @martijnwalraven @jbaxleyiii @trevor-scheer @hwillson

Author: abernix

package-lock.json

@@ -90,7 +90,6 @@
     "ts-jest": "^23.1.4",
     "ts-loader": "^4.5.0",
     "ts-node": "^7.0.1",
-    "tsc-watch": "^1.0.30",
     "tsconfig-paths-webpack-plugin": "^3.2.0",
     "tslib": "^1.9.3",
     "typescript": "^3.0.3",