refactor(gitlab): use markdown not html

lib/platform/gitlab/index.js

 const is = require('@sindresorhus/is');
 const addrs = require('email-addresses');
-const showdown = require('showdown');
 
 const get = require('./gl-got-wrapper');
 const hostRules = require('../../util/host-rules');
 
-const converter = new showdown.Converter();
-converter.setFlavor('github');
-
 let config = {};
 
 module.exports = {
@@ -727,17 +723,7 @@ async function mergePr(iid) {
 }
 
 function getPrBody(input) {
-  // Convert to HTML using GitHub-flavoured markdown as it is more feature-rich than GitLab's flavour
-  return converter
-    .makeHtml(input)
-    .replace(/Pull Request/g, 'Merge Request')
-    .replace(/PR/g, 'MR')
-    .replace(
-      `<p><details><br />\n<summary>Release Notes</summary></p>`,
-      '\n<details>\n\n<summary>Release Notes</summary>\n\n'
-    )
-    .replace('<p></details></p>', '\n</details>\n');
-  // TODO: set maximum length
+  return input.replace(/Pull Request/g, 'Merge Request').replace(/PR/g, 'MR');
 }
 
 // Generic File operations

test/platform/gitlab/__snapshots__/index.spec.js.snap

@@ -243,7 +243,7 @@ Object {
 }
 `;
 
-exports[`platform/gitlab getPrBody(input) returns updated pr body 1`] = `"<p><a href=\\"https://github.com/foo/bar/issues/5\\">https://github.com/foo/bar/issues/5</a> plus also <a href=\\"https://github.com/foo/bar/issues/5\\">a link</a></p>"`;
+exports[`platform/gitlab getPrBody(input) returns updated pr body 1`] = `"https://github.com/foo/bar/issues/5 plus also [a link](https://github.com/foo/bar/issues/5)"`;
 
 exports[`platform/gitlab getPrFiles() returns files 1`] = `
 Array [