include: doc: move documentation from .h file to doxygen file

doc/doxygen/chapters/api/data_interfaces.doxy

@@ -451,6 +451,8 @@ offset in the vector
 number of elements on the x-axis of the vector
 \var size_t starpu_vector_interface::elemsize
 size of the elements of the vector
+\var uint32_t starpu_vector_interface::slice_base
+vector slice base, used by the StarPU OpenMP runtime support
 
 \fn uint32_t starpu_vector_get_nx(starpu_data_handle_t handle)
 \ingroup API_Data_Interfaces

include/starpu_data_interfaces.h

@@ -255,7 +255,6 @@ struct starpu_vector_interface
 	uint32_t nx;
 	size_t elemsize;
 
-	/* vector slice base, used by the StarPU OpenMP runtime support */
 	uint32_t slice_base;
 };