Remove superfluous parens

[[Imported from SVN: r12870]]

dune/fufem/assemblers/localassemblers/viscosityassembler.hh

@@ -33,7 +33,7 @@ class ViscosityAssembler
     SymmetricTensor<dim> strainToStress(const SymmetricTensor<dim>& strain) const {
 
             SymmetricTensor<dim> stress = strain;
-            stress *= 2*(muShear_);
+            stress *= 2*muShear_;
             stress.addToDiag((muBulk_-(2.0/3.0)*muShear_) * strain.trace());
             return stress;
     }