platforms/drm: Drop stream operator for DrmOutput

There is already one that works for all AbstractOutput classes and
properly restores the state of QDebug.

src/plugins/platforms/drm/drm_output.cpp

@@ -885,10 +885,3 @@ bool DrmOutput::setGammaRamp(const GammaRamp &gamma)
 }
 
 }
-
-QDebug& operator<<(QDebug& s, const KWin::DrmOutput *output)
-{
-    if (!output)
-        return s.nospace() << "DrmOutput()";
-    return s.nospace() << "DrmOutput(" << output->name() << ", crtc:" << output->crtc() << ", connector:" << output->connector() << ", geometry:" << output->geometry() << ')';
-}

src/plugins/platforms/drm/drm_output.h

@@ -177,7 +177,4 @@ private:
 
 Q_DECLARE_METATYPE(KWin::DrmOutput*)
 
-QDebug& operator<<(QDebug& stream, const KWin::DrmOutput *);
-
 #endif
-