/usr/share/applications/apturl.desktop is in apturl-common 0.5.2ubuntu14.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 | [Desktop Entry]
Name=AptURL
Exec=apturl %u
Type=Application
NoDisplay=true
Categories=System;
MimeType=x-scheme-handler/apt;
|