Remove conventional-changelog

This addon had two approaches in place to manage the changelog,
conventional-changelog and release-it-lerna-changelog. This commit
consolidates this into one: release-it-lerna-changelog, as already
documented in RELEASE.md.

Author: lukemelia

package.json

@@ -26,9 +26,7 @@
     "start": "ember serve",
     "test": "npm-run-all lint test:*",
     "test:ember": "ember test",
-    "test:ember-compatibility": "ember try:each",
-    "update-changelog": "conventional-changelog -i CHANGELOG.md -r 0 -s",
-    "version": "yarn run update-changelog && git add CHANGELOG.md"
+    "test:ember-compatibility": "ember try:each"
   },
   "dependencies": {
     "broccoli-funnel": "^3.0.3",
@@ -46,8 +44,6 @@
     "@glimmer/tracking": "^1.0.4",
     "babel-eslint": "^10.1.0",
     "broccoli-asset-rev": "^3.0.0",
-    "conventional-changelog": "^1.1.4",
-    "conventional-changelog-cli": "^1.3.2",
     "ember-auto-import": "^1.12.0",
     "ember-cli": "~3.28.6",
     "ember-cli-dependency-checker": "^3.2.0",