[platforms/x11] Delete duplicate doxygen comments in X11Output

Summary:
geometry(), refreshRate(), and gammaRampSize() are already documented in
AbstractOutput class.

Test Plan: Compiles.

Reviewers: #kwin, apol

Reviewed By: apol

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D23481

plugins/platforms/x11/standalone/x11_output.h

@@ -44,21 +44,13 @@ public:
 
     QString name() const override;
     void setName(QString set);
-    /**
-     * The geometry of this output in global compositor co-ordinates (i.e scaled)
-     */
+
     QRect geometry() const override;
     void setGeometry(QRect set);
 
-    /**
-     * Current refresh rate in 1/μs = 1000/ms.
-     */
     int refreshRate() const override;
     void setRefreshRate(int set);
 
-    /**
-     * The size of gamma lookup table.
-     */
     int gammaRampSize() const override;
     bool setGammaRamp(const GammaRamp &gamma) override;