modernize: delete redundant void args

Summary:
Redundant void args are deleted with clang-tidy.
See https://clang.llvm.org/extra/clang-tidy/checks/modernize-redundant-void-arg.html

Reviewers: #breeze, mart

Reviewed By: mart

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D11636