[effects] Drop loading shadow config from MagicLamp

Summary:
This has basically been dead code for ages. The Shadow effect got
dropped in an early 4.x version. We shouldn't transform the window based
on old shadow values, so completely removed.

Reviewers: #kwin, #plasma

Subscribers: plasma-devel, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D3339