plugins/screencast: Don't make effects opengl context current

This makes eglSwapBuffers() fail with per screen rendering enabled. In
long term, the screencast plugin has to create its own OpenGL context
and capture window frames after a compositing cycle has been performed.
However, it's currently tricky to do because of monitor screencasting.

plugins/screencast/screencastmanager.cpp

@@ -70,7 +70,6 @@ private:
         if (m_damagedRegion.isEmpty()) {
             return;
         }
-        effects->makeOpenGLContextCurrent();
         QSharedPointer<GLTexture> frameTexture(m_toplevel->effectWindow()->sceneWindow()->windowTexture());
         const bool wasYInverted = frameTexture->isYInverted();
         frameTexture->setYInverted(false);