regression: fixed ARDUINO_USER_AGENT pollution / resolve compile-sk…

…etch GH action failure on Teensy (#2669)

* Removed useless gRPCClientUnknown tag

* 'task build' now uses a compliant semver notation

* Revert "'task build' now uses a compliant semver notation"

This reverts commit 7f8ad1f.

commands/instances.go

@@ -67,9 +67,6 @@ func (s *arduinoCoreServerImpl) Create(ctx context.Context, req *rpc.CreateReque
 	if md, ok := metadata.FromIncomingContext(ctx); ok {
 		userAgent = strings.Join(md.Get("user-agent"), " ")
 	}
-	if userAgent == "" {
-		userAgent = "gRPCClientUnknown/0.0.0"
-	}
 
 	// Setup downloads directory
 	downloadsDir := s.settings.DownloadsDir()