Use do_remove_returns instead of remove_returns

This ensures that this pass is done only once and is shown in the
logging.

Author: thomasspriggs

regression/goto-instrument/constant-propagation-function-call/test.desc

@@ -3,6 +3,7 @@ main.c
 --constant-propagator
 ^EXIT=10$
 ^SIGNAL=0$
+Removing returns
 VERIFICATION FAILED
 ASSIGN main\:\:1\:\:a \:\= 4
 ASSERT ¬\(main::1::b ≥ 0\) ∨ main::1::b ≥ 5

src/goto-instrument/goto_instrument_parse_options.cpp

@@ -1285,7 +1285,7 @@ void goto_instrument_parse_optionst::instrument_goto_program()
   if(cmdline.isset("constant-propagator"))
   {
     do_indirect_call_and_rtti_removal();
-    remove_returns(goto_model);
+    do_remove_returns();
 
     log.status() << "Propagating Constants" << messaget::eom;