Remove all proposal-related code

We're not using proposals at the moment, so it's just in the way.

tests/unit/controllers/proposals/new-test.js

@@ -1,12 +0,0 @@
-import { module, test } from 'qunit';
-import { setupTest } from 'ember-qunit';
-
-module('Unit | Controller | proposals/new', function(hooks) {
-  setupTest(hooks);
-
-  // Replace this with your real tests.
-  test('it exists', function(assert) {
-    let controller = this.owner.lookup('controller:proposals/new');
-    assert.ok(controller);
-  });
-});