build: Don't check for supported Go version

One thing less to maintain, and you can discover for yourself if it
builds or not.

build.go

@@ -203,8 +203,6 @@ func init() {
 	targets["syncthing"] = syncthingPkg
 }
 
-const minGoVersion = 1.5
-
 func main() {
 	log.SetOutput(os.Stdout)
 	log.SetFlags(0)
@@ -220,9 +218,6 @@ func main() {
 		setGoPath()
 	}
 
-	// We use Go 1.5+ vendoring.
-	os.Setenv("GO15VENDOREXPERIMENT", "1")
-
 	// Set path to $GOPATH/bin:$PATH so that we can for sure find tools we
 	// might have installed during "build.go setup".
 	os.Setenv("PATH", fmt.Sprintf("%s%cbin%c%s", os.Getenv("GOPATH"), os.PathSeparator, os.PathListSeparator, os.Getenv("PATH")))
@@ -230,7 +225,6 @@ func main() {
 	parseFlags()
 
 	checkArchitecture()
-	goVersion, _ = checkRequiredGoVersion()
 
 	// Invoking build.go with no parameters at all builds everything (incrementally),
 	// which is what you want for maximum error checking during development.
@@ -355,27 +349,6 @@ func parseFlags() {
 	flag.Parse()
 }
 
-func checkRequiredGoVersion() (float64, bool) {
-	re := regexp.MustCompile(`go(\d+\.\d+)`)
-	ver := runtime.Version()
-	if m := re.FindStringSubmatch(ver); len(m) == 2 {
-		vs := string(m[1])
-		// This is a standard go build. Verify that it's new enough.
-		f, err := strconv.ParseFloat(vs, 64)
-		if err != nil {
-			log.Printf("*** Couldn't parse Go version out of %q.\n*** This isn't known to work, proceed on your own risk.", vs)
-			return 0, false
-		}
-		if f < minGoVersion {
-			log.Fatalf("*** Go version %.01f is less than required %.01f.\n*** This is known not to work, not proceeding.", f, minGoVersion)
-		}
-		return f, true
-	}
-
-	log.Printf("*** Unknown Go version %q.\n*** This isn't known to work, proceed on your own risk.", ver)
-	return 0, false
-}
-
 func setup() {
 	packages := []string{
 		"github.com/alecthomas/gometalinter",