test: fix return.go to not use fallthrough in a type switch

The gc compiler only gives an error about fallthrough in a
type switch if it has not given any errors in an earlier pass.
Remove all functions in this test that use fallthrough in a
type switch because they don't test anything useful and they
cause gccgo to give unexpected errors.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/12614043

test/return.go

@@ -666,17 +666,6 @@ func _() int {
 	}
 }
 
-func _() int {
-	print(1)
-	switch x.(type) {
-	case int:
-		print(2)
-		fallthrough
-	default:
-		return 4
-	}
-}
-
 // if no default or some case doesn't terminate, switch is no longer okay
 
 func _() int {
@@ -708,17 +697,6 @@ func _() int {
 	}
 } // ERROR "missing return"
 
-func _() int {
-	print(1)
-	switch x.(type) {
-	case int:
-		print(2)
-		fallthrough
-	case float64:
-		return 4
-	}
-} // ERROR "missing return"
-
 func _() int {
 	print(1)
 	switch x.(type) {
@@ -1356,16 +1334,6 @@ func _() int {
 	}
 }
 
-func _() int {
-	switch x.(type) {
-	case int:
-		print(2)
-		fallthrough
-	default:
-		return 4
-	}
-}
-
 // if no default or some case doesn't terminate, switch is no longer okay
 
 func _() int {
@@ -1394,16 +1362,6 @@ func _() int {
 	}
 } // ERROR "missing return"
 
-func _() int {
-	switch x.(type) {
-	case int:
-		print(2)
-		fallthrough
-	case float64:
-		return 4
-	}
-} // ERROR "missing return"
-
 func _() int {
 	switch x.(type) {
 	case int:
@@ -2102,17 +2060,6 @@ var _ = func() int {
 	}
 }
 
-var _ = func() int {
-	print(1)
-	switch x.(type) {
-	case int:
-		print(2)
-		fallthrough
-	default:
-		return 4
-	}
-}
-
 // if no default or some case doesn't terminate, switch is no longer okay
 
 var _ = func() int {
@@ -2144,17 +2091,6 @@ var _ = func() int {
 	}
 } // ERROR "missing return"
 
-var _ = func() int {
-	print(1)
-	switch x.(type) {
-	case int:
-		print(2)
-		fallthrough
-	case float64:
-		return 4
-	}
-} // ERROR "missing return"
-
 var _ = func() int {
 	print(1)
 	switch x.(type) {
@@ -2792,16 +2728,6 @@ var _ = func() int {
 	}
 }
 
-var _ = func() int {
-	switch x.(type) {
-	case int:
-		print(2)
-		fallthrough
-	default:
-		return 4
-	}
-}
-
 // if no default or some case doesn't terminate, switch is no longer okay
 
 var _ = func() int {
@@ -2830,16 +2756,6 @@ var _ = func() int {
 	}
 } // ERROR "missing return"
 
-var _ = func() int {
-	switch x.(type) {
-	case int:
-		print(2)
-		fallthrough
-	case float64:
-		return 4
-	}
-} // ERROR "missing return"
-
 var _ = func() int {
 	switch x.(type) {
 	case int: