Cleanup invariants in remove_unused_functions

Author: hannes-steffenhagen-diffblue

src/goto-programs/remove_unused_functions.cpp

@@ -77,9 +77,6 @@ void find_used_functions(
         {
           const code_function_callt &call = to_code_function_call(it->code);
 
-          // check that this is actually a simple call
-          assert(call.function().id()==ID_symbol);
-
           const irep_idt &identifier =
             to_symbol_expr(call.function()).get_identifier();