Remove two unused parameters

'thickness' and 'kappa' are parameters in Cosserat shell models.
They are not necessary for bulk models.  Hence remove them.

test/cosseratcontinuumtest.cc

@@ -185,13 +185,11 @@ int main (int argc, char *argv[])
   // ////////////////////////////
 
   ParameterTree parameters;
-  parameters["thickness"] = "0.1";
   parameters["mu"] = "1";
   parameters["lambda"] = "1";
   parameters["mu_c"] = "1";
   parameters["L_c"] = "0.1";
   parameters["q"] = "2";
-  parameters["kappa"] = "1";
   parameters["b1"] = "1";
   parameters["b2"] = "1";
   parameters["b3"] = "1";