Remove two unused labels

doc/manual/dune-functions-manual.tex

@@ -372,7 +372,6 @@ reuse existing algorithms that expect to operate on those subtrees in more compl
 
 
 \subsection{Indexing basis functions by multi-indices}
-\label{sec:basis_ordering}
 
 To work with the basis of a finite element space, the basis vectors need to be indexed.  Indexing the basis functions
 is what allows to address the corresponding vector and matrix coefficients in suitable vector and matrix data structures.
@@ -583,7 +582,6 @@ to the number of direct children of the node indexed by $I$.
 
 
 \subsection{Rule-based construction of multi-indices}
-\label{sec:basis_ordering}
 
 While \dunemodule{dune-functions} allows to use arbitrary index trees
 to enumerate the basis functions, there are some important generic constructions