Remove find modules provided by ECM

Summary:
This matters specifically here as kdelibs4support installs them and
adds them to the module search path, which can interfere with the
newer ones provided by ECM (see e.g. D18943).

Reviewers: apol

Reviewed By: apol

Subscribers: cgiboudeaux, apol, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D19527