DevTools: [Documentation] Remove approximate URL-creating method

Now we use only data downloaded from webplatform.org to create a URL for the documentation. 
Auto-loading will be removed in next patch when we add an extension for documentation module.

BUG=391593

Review URL: https://codereview.chromium.org/559123002

git-svn-id: svn://svn.chromium.org/blink/trunk@182142 bbb929c8-8fbe-4397-9dbb-9b2b20218538