Remove outdated script for handling translations

Summary:
The files were relevant when the modules lived in its own repository.
Translations are now included in the plasma-desktop tarball by the
release scripts.

The README.md contains some other outdated informations, but they are
out of scope for this change.

Reviewers: Plasma, davidedmundson

Reviewed By: Plasma, davidedmundson

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D3542