removed old shader_kernel

src/canvas_shader.rs

@@ -47,7 +47,7 @@ impl CanvasShader {
         (vertex_shader_path, fragment_shader_path)
     }
 
-    pub fn get_pipeline(&mut self) -> Arc<dyn GraphicsPipelineAbstract + Sync + Send> {
+    pub fn get_pipeline(&self) -> Arc<dyn GraphicsPipelineAbstract + Sync + Send> {
         self.graphics_pipeline.clone().unwrap()
     }