Remove tk sync example from help command

Signed-off-by: Manuel Morejon <manuel@mmorejon.io>

cmd/tk/main.go

@@ -53,9 +53,6 @@ var rootCmd = &cobra.Command{
   # List GitRepository sources and their status
   tk get sources git
 
-  # Trigger a GitRepository source sync
-  tk sync source git webapp-latest
-
   # Export GitRepository sources in YAML format
   tk export source git --all > sources.yaml