Fix MSVC error in cpp_typedef.i

MSVC in C++20 mode complains:

error C7626: unnamed class used in typedef name cannot declare members other than non-static data members, member enumerations, or member classes

The struct member in question isn't actually used by the testcase, so
just remove it.

Examples/test-suite/cpp_typedef.i

@@ -30,7 +30,6 @@ public:
 // Test that the correct types are used for typedef struct declarations
 typedef struct {
   int something;
-  void m() {}
 } UnnamedStruct;
 
 typedef struct NamedStruct {