The new Xcode is
.app and all the package contents are with it, inside the applications folder. Can I just delete
You can delete this folder. The new /Developer is located in /Applications/Xcode.app/Contents/Developer, so /Developer can be deleted.
As of Xcode 4.3, the /Developer directory is no longer needed.
Xcode prior to 4.3, which is when Apple transitioned to a single repackaged
.app for their developer tools, also shipped with an
uninstall-devtools command line utility. It takes a look at any receipts of Xcode installs on your system and reports that it's removing things like caches, as well. Invoke as:
to do a complete removal of all pre-4.3 Xcode remnants on your system.