Remove Makefile from all intree extensions

- Makefiles are not really common (rightly so) in JS projects and script
  entries in the package.json are good enough and what they're there
  for.

- Move to using yarn for installing dependencies and running scripts as
  that is what we mostly use for the rest of the project.

- Move from using make syntax to a dedicated script for building and
  testing extensions.

Signed-off-by: Sebastian Malton <sebastian@malton.name>

extensions/support-page/Makefile

@@ -1,8 +0,0 @@
-install-deps:
-	yarn install
-
-build: install-deps
-	yarn run build
-
-test:
-	yarn run test

extensions/support-page/package.json

@@ -7,7 +7,7 @@
   "scripts": {
     "build": "webpack -p",
     "dev": "webpack --watch",
-    "test": "echo NO TESTS"
+    "test": "jest --passWithNoTests --env=jsdom src $@"
   },
   "dependencies": {},
   "devDependencies": {