bump google.golang.org/grpc v1.23.0

full diff: https://github.com/grpc/grpc-go/compare/v1.20.1...v1.23.0

This update contains security fixes:

- transport: block reading frames when too many transport control frames are queued (grpc/grpc-go#2970)
  - Addresses CVE-2019-9512 (Ping Flood), CVE-2019-9514 (Reset Flood), and CVE-2019-9515 (Settings Flood).

Other changes can be found in the release notes:
https://github.com/grpc/grpc-go/releases/tag/v1.23.0

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

vendor/google.golang.org/grpc/internal/envconfig/envconfig.go

@@ -25,40 +25,11 @@ import (
 )
 
 const (
-	prefix              = "GRPC_GO_"
-	retryStr            = prefix + "RETRY"
-	requireHandshakeStr = prefix + "REQUIRE_HANDSHAKE"
-)
-
-// RequireHandshakeSetting describes the settings for handshaking.
-type RequireHandshakeSetting int
-
-const (
-	// RequireHandshakeOn indicates to wait for handshake before considering a
-	// connection ready/successful.
-	RequireHandshakeOn RequireHandshakeSetting = iota
-	// RequireHandshakeOff indicates to not wait for handshake before
-	// considering a connection ready/successful.
-	RequireHandshakeOff
+	prefix   = "GRPC_GO_"
+	retryStr = prefix + "RETRY"
 )
 
 var (
 	// Retry is set if retry is explicitly enabled via "GRPC_GO_RETRY=on".
 	Retry = strings.EqualFold(os.Getenv(retryStr), "on")
-	// RequireHandshake is set based upon the GRPC_GO_REQUIRE_HANDSHAKE
-	// environment variable.
-	//
-	// Will be removed after the 1.18 release.
-	RequireHandshake = RequireHandshakeOn
 )
-
-func init() {
-	switch strings.ToLower(os.Getenv(requireHandshakeStr)) {
-	case "on":
-		fallthrough
-	default:
-		RequireHandshake = RequireHandshakeOn
-	case "off":
-		RequireHandshake = RequireHandshakeOff
-	}
-}