fix: drop preformatted changelog

No longer supporting preformatted (markdown) changelog input for templates.

BREAKING CHANGE: Preformatted {{changeloge}} no longer supported in PR body template.
Generate changelog using handlebars as in the default templtaes.

lib/workers/pr/index.js

@@ -65,8 +65,6 @@ async function ensurePr(upgrades, logger) {
     );
     // Store changelog markdown for backwards compatibility
     if (logJSON) {
-      config.changelog =
-        config.changelog || changelogHelper.getMarkdown(logJSON);
       upgrade.githubName = logJSON.project.github;
       upgrade.releases = [];
       logJSON.versions.forEach(version => {