Remove a pointless 'sym' and corresponding comment.

Because trace(sym(A)) == trace(A)

[[Imported from SVN: r8568]]

dune/gfe/cosseratenergystiffness.hh

@@ -318,8 +318,7 @@ public:
             
         return mu_ * sym(RT_DR3).frobenius_norm2()
                + mu_c_ * skew(RT_DR3).frobenius_norm2()
-               /** \todo Is this sym correct?  It is in the paper, but not in the notes */
-               + mu_*lambda_/(2*mu_+lambda_) * traceSquared(sym(RT_DR3));
+               + mu_*lambda_/(2*mu_+lambda_) * traceSquared(RT_DR3);
     }
 
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