They do roughly the same as before, but there are differences. You should switch to the new methods instead: Since Plone 3 there have been several breaking changes relating to content type icon rendering.
Plone 3 Content type icons where rendered as HTML tags, which were rendered with methods from …: ) and other locations was more then deprecated - it is obsolete and confusing and is getting removed.
Note that some variables are still globally available, the most important being context, view and template.
This was always only partial, so you could not rely on it to fully cleanup the site. Best practice is to create an uninstall profile for all your packages.
If you were relying on this automatic cleanup, you need to add extra files to clean it up yourself.
Only one indexing operation is done per object on any transaction.
Some tests and features might expect that objects are being indexed/reindexed/unindexed right away.
Products providing icons for CMF actions should now register them using the 'icon_expr' setting on the action itself, rather than using the separate action icons tool.