Fix broken mesh2d (#15838)

Forgot to clean this up when I was still trying to figure out what was
broken.

Closes #15835.

crates/bevy_sprite/src/mesh2d/material.rs

@@ -17,7 +17,7 @@ use bevy_ecs::{
 };
 use bevy_math::FloatOrd;
 use bevy_reflect::{prelude::ReflectDefault, Reflect};
-use bevy_render::sync_world::{MainEntity, MainEntityHashMap};
+use bevy_render::sync_world::MainEntityHashMap;
 use bevy_render::view::RenderVisibleEntities;
 use bevy_render::{
  mesh::{MeshVertexBufferLayoutRef, RenderMesh},
@@ -501,8 +501,7 @@ impl<P: PhaseItem, M: Material2d, const I: usize> RenderCommand<P>
  ) -> RenderCommandResult {
  let materials = materials.into_inner();
  let material_instances = material_instances.into_inner();
- let Some(material_instance) = material_instances.get(&MainEntity::from(item.entity()))
- else {
+ let Some(material_instance) = material_instances.get(&item.main_entity()) else {
  return RenderCommandResult::Skip;
  };
  let Some(material2d) = materials.get(*material_instance) else {