docs/user: Remove duplicate "ingroup interface" from layout docs.

Since the "Layout" group is a member of the "Interface" group,
Doxygen automatically adds the "Interface" group to all pages
in the "Layout" group, meaning that having an explicit "ingroup Interface"
created duplicate group tags.

docs/user/interface/TwoDimensionalLayout.dox

@@ -13,7 +13,6 @@
 
 /*!
 	\file TwoDimensionalLayout.h
-	\ingroup interface
 	\ingroup layout
 	\ingroup libbe
 	\brief Defines the BTwoDimensionalLayout class.
@@ -22,7 +21,6 @@
 
 /*!
 	\class BTwoDimensionalLayout
-	\ingroup interface
 	\ingroup layout
 	\ingroup libbe
 	\brief Abstract BLayout subclass arranging items within rows and columns.