[Sketcher] make more pointers to the UI std::unique_ptr

addendum to PR #4362

(Same as PR #4293, just for Sketcher

as noted in https://github.com/FreeCAD/FreeCAD/pull/4271#discussion_r554673632
the pointer to the UI should be a unique pointer.

This PR does this for all Sketcher dialogs that don't already use a unique_ptr.)

src/Mod/Sketcher/Gui/SketchRectangularArrayDialog.cpp

@@ -53,7 +53,6 @@ SketchRectangularArrayDialog::SketchRectangularArrayDialog(void)
 
 SketchRectangularArrayDialog::~SketchRectangularArrayDialog()
 {
-    delete ui;
 }
 
 void SketchRectangularArrayDialog::accept()