Don't include struct member types in mangled string.

Not only was this quite verbose, it was unnecessary since we do type
equality by name.  This also needed to be fixed before we could
handle structs declared like "struct Foo;", when we then e.g. have
other structs with Foo * members.

type.cpp

@@ -1912,10 +1912,7 @@ StructType::Mangle() const {
         ret += "_c_";
     ret += variability.MangleString();
 
-    ret += name + std::string("]<");
-    for (unsigned int i = 0; i < elementTypes.size(); ++i)
-        ret += GetElementType(i)->Mangle();
-    ret += ">";
+    ret += name + std::string("]");
     return ret;
 }