remove go build directive for older go version

Go 1.4 is too old and should be dropped safely.

Signed-off-by: bin liu <liubin0329@gmail.com>

registry/handlers/basicauth.go

@@ -1,6 +1,3 @@
-//go:build go1.4
-// +build go1.4
-
 package handlers
 
 import (

registry/handlers/basicauth_prego14.go

@@ -1,42 +0,0 @@
-//go:build !go1.4
-// +build !go1.4
-
-package handlers
-
-import (
-	"encoding/base64"
-	"net/http"
-	"strings"
-)
-
-// NOTE(stevvooe): This is basic auth support from go1.4 present to ensure we
-// can compile on go1.3 and earlier.
-
-// BasicAuth returns the username and password provided in the request's
-// Authorization header, if the request uses HTTP Basic Authentication.
-// See RFC 2617, Section 2.
-func basicAuth(r *http.Request) (username, password string, ok bool) {
-	auth := r.Header.Get("Authorization")
-	if auth == "" {
-		return
-	}
-	return parseBasicAuth(auth)
-}
-
-// parseBasicAuth parses an HTTP Basic Authentication string.
-// "Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==" returns ("Aladdin", "open sesame", true).
-func parseBasicAuth(auth string) (username, password string, ok bool) {
-	if !strings.HasPrefix(auth, "Basic ") {
-		return
-	}
-	c, err := base64.StdEncoding.DecodeString(strings.TrimPrefix(auth, "Basic "))
-	if err != nil {
-		return
-	}
-	cs := string(c)
-	s := strings.IndexByte(cs, ':')
-	if s < 0 {
-		return
-	}
-	return cs[:s], cs[s+1:], true
-}