tutorial: remove all plugins but identity

gst-plugin-tutorial/src/lib.rs

@@ -19,17 +19,11 @@ extern crate num_traits;
 extern crate once_cell;
 
 mod identity;
-mod progressbin;
-mod rgb2gray;
-mod sinesrc;
 
 // Plugin entry point that should register all elements provided by this plugin,
 // and everything else that this plugin might provide (e.g. typefinders or device providers).
 fn plugin_init(plugin: &gst::Plugin) -> Result<(), glib::BoolError> {
-    rgb2gray::register(plugin)?;
-    sinesrc::register(plugin)?;
     identity::register(plugin)?;
-    progressbin::register(plugin)?;
     Ok(())
 }