all: rollback to old interpolation (step 3) (#16380)

vlib/builtin/string_test.v

@@ -849,11 +849,6 @@ fn test_raw_inter() {
 	assert s.contains('$')
 }
 
-fn test_new_inter() {
-	// world := 'world'
-	// assert 'hello {world}' == 'hello world'
-}
-
 fn test_c_r() {
 	// This used to break because of r'' and c''
 	c := 42