Remove mk2rbc's support for using a product name

Now that the product and board config pass makefiles
to mk2rbc, we don't need to support passing a product
name.

Bug: 201700692
Test: Manually
Change-Id: I787f0f98bc5ab3cefeefb7af8d342aba84769925

mk2rbc/cmd/mk2rbc.go

@@ -155,22 +155,12 @@ func main() {
 
 	// Convert!
 	files := flag.Args()
-	productConfigMap := buildProductConfigMap()
 	if *allInSource {
+		productConfigMap := buildProductConfigMap()
 		for _, path := range productConfigMap {
 			files = append(files, path)
 		}
 	}
-	for i, file := range files {
-		if _, err := os.Stat(file); os.IsNotExist(err) {
-			temp, ok := productConfigMap[file]
-			if ok {
-				files[i] = temp
-			} else {
-				quit(fmt.Errorf("%s is neither a product makefile nor a product name", file))
-			}
-		}
-	}
 	ok := true
 	for _, mkFile := range files {
 		ok = convertOne(mkFile) && ok