Remove stray todo from gvpart.desktop

Summary:
After David fixed the global mimetype brokenness/warning in
e631f016, Aurélien removed the TODO in 3f3a8fa8 for `gwenview`.
Let's do this for `gvpart` too.

Not sure why f5031f90 introduced `KRL` in the first place, it does
not seem to be used for images anymore today.

Test Plan:
File which is installed on user's systems not used anymore for asking
developer related question ;)

Reviewers: ngraham

Reviewed By: ngraham

Differential Revision: https://phabricator.kde.org/D8769