Remove the line #undef overwrite

Newer versions of ADOL-C do not define 'overwrite' anymore, hence there
is no risk of macro clashing.

[[Imported from SVN: r9798]]

cosserat-continuum.cc

@@ -9,7 +9,6 @@
 #include <adolc/adouble.h>
 #include <adolc/drivers/drivers.h>    // use of "Easy to Use" drivers
 #include <adolc/taping.h>
-#undef overwrite  // stupid: ADOL-C sets this to 1, so the name cannot be used
 
 #include <dune/gfe/adolcnamespaceinjections.hh>
 #include <dune/common/bitsetvector.hh>

dune/gfe/localgeodesicfeadolcstiffness.hh

@@ -6,8 +6,6 @@
 // gradient(.) and hessian(.)
 #include <adolc/taping.h>             // use of taping
 
-#undef overwrite  // stupid: ADOL-C sets this to 1, so the name cannot be used
-
 #include <dune/gfe/adolcnamespaceinjections.hh>
 
 #include <dune/common/fmatrix.hh>