/usr/share/kservices5/searchproviders/usource.desktop is in kubuntu-web-shortcuts 17.04ubuntu1.
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 8 | [Desktop Entry]
Charset=
Hidden=false
Keys=usource,usrc
Name=Ubuntu Source Packages
Query=https://launchpad.net/ubuntu/+source/\\{@}
ServiceTypes=SearchProvider
Type=Service
|