[Sketch] fix these issues:

- missing menu entry for centered rectangle
- typo
- uniform word casing
- duplicated accel key
- remove superfluous comment

src/Mod/Sketcher/Gui/Workbench.cpp

@@ -289,9 +289,6 @@ inline void SketcherAddWorkbenchGeometries(T& geom)
             /*<< "Sketcher_CreateDraftLine"*/;
 }
 
-//template <typename T>
-//void SketcherAddWorkbenchConstraints(T& cons);
-
 template <typename T>
 inline void SketcherAddWorkbenchConstraints(T& cons);