actually remove unused ksnrc file

Summary:
this file is not getting installed for years. it was dropped in
836486fbfd3f8256e9749c15d0874a9a780a0471 but unfortunately that commit
neglected to also drop the file from git.
in order to resolve this dissonance between git and install -> delete it
(it's still in the history anyway, should we need to recover it at some
point)

Reviewers: apol, davidedmundson

Reviewed By: davidedmundson

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D18428