turn off tracing by default, change golden (#381)

* turn off tracing by default, change golden

* Update executable_semantics/main.cpp

Co-authored-by: Jon Meow <46229924+jonmeow@users.noreply.github.com>

* Update executable_semantics/main.cpp

Co-authored-by: Jon Meow <46229924+jonmeow@users.noreply.github.com>

* merge with trunk, update goldens

Co-authored-by: Jon Meow <46229924+jonmeow@users.noreply.github.com>

executable_semantics/testdata/zero.golden

@@ -1,72 +1 @@
-********** source program **********
-fn main () -> Int {
-return 0;
-
-}
-********** type checking **********
---- step exp Int --->
---- step exp Int --->
-
-********** type checking complete **********
-fn main () -> Int {
-return 0;
-}
-********** starting execution **********
-********** initializing globals **********
---- step exp () --->
-********** calling main function **********
-{
-stack: top{main()<-1>}
-heap: fun<main>, 
-env: main: fun<main>, 
-}
---- step exp main() --->
-{
-stack: top{main<-1> :: main()<0>}
-heap: fun<main>, 
-env: main: fun<main>, 
-}
---- step exp main --->
-{
-stack: top{fun<main><-1> :: main()<0>}
-heap: fun<main>, 
-env: main: fun<main>, 
-}
---- handle value fun<main> with main()<1>(fun<main>,) --->
-{
-stack: top{()<-1> :: main()<1>(fun<main>,)}
-heap: fun<main>, 
-env: main: fun<main>, 
-}
---- step exp () --->
-{
-stack: top{()<-1> :: main()<1>(fun<main>,)}
-heap: fun<main>, 
-env: main: fun<main>, 
-}
---- handle value () with main()<2>(fun<main>,(),) --->
-pattern_match((), ())
-{
-stack: main{return 0;<-1>} :: top{}
-heap: fun<main>, 
-env: main: fun<main>, 
-}
---- step stmt return 0; --->
-{
-stack: main{0<-1> :: return 0;<0>} :: top{}
-heap: fun<main>, 
-env: main: fun<main>, 
-}
---- step exp 0 --->
-{
-stack: main{0<-1> :: return 0;<0>} :: top{}
-heap: fun<main>, 
-env: main: fun<main>, 
-}
---- handle value 0 with return 0;<1>(0,) --->
-{
-stack: top{0<-1>}
-heap: fun<main>, 
-env: main: fun<main>, 
-}
 result: 0