[potd dataengine] Turn prodiver plugin metadata into json files
Summary:
The desktop files are only used at buildtime, so given the existing support
of scripty for plugin metadata JSON files, no need for the additional format
conversion during the build.
Test Plan: All plugins still load and build.
Reviewers: xuetianweng
Subscribers: ltoscano, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D11954