Fix staging buffer required size calculation (fixes bevyengine#1056)

The required staging buffer size is already properly calculated in
prepare_staging_buffers(). Whenever a resize was needed, this value
got overwritten by set_required_staging_buffer_size_to_max(), which
computed the wrong (smaller) size. This in turn prevented the staging
buffers from being resized in resize_staging_buffer().

By removing set_required_staging_buffer_size_to_max() entiery, the value
from prepare_staging_buffers() is used.

crates/bevy_render/src/render_graph/nodes/render_resources_node.rs

@@ -208,17 +208,6 @@ where
  resized
  }
 
- fn set_required_staging_buffer_size_to_max(&mut self) {
- let mut new_size = 0;
- for buffer_array in self.buffer_arrays.iter() {
- if let Some(buffer_array) = buffer_array {
- new_size += buffer_array.item_size * buffer_array.len;
- }
- }
-
- self.required_staging_buffer_size = new_size;
- }
-
  /// Update the staging buffer to provide enough space to copy data to target buffers.
  fn resize_staging_buffer(&mut self, render_resource_context: &dyn RenderResourceContext) {
  // TODO: allow staging buffer to scale down
@@ -484,9 +473,6 @@ fn render_resources_node_system<T: RenderResources>(
  }
 
  let resized = uniform_buffer_arrays.resize_buffer_arrays(render_resource_context);
- if resized {
- uniform_buffer_arrays.set_required_staging_buffer_size_to_max()
- }
  uniform_buffer_arrays.resize_staging_buffer(render_resource_context);
 
  if let Some(staging_buffer) = state.uniform_buffer_arrays.staging_buffer {
@@ -697,9 +683,6 @@ fn asset_render_resources_node_system<T: RenderResources + Asset>(
  }
 
  let resized = uniform_buffer_arrays.resize_buffer_arrays(render_resource_context);
- if resized {
- uniform_buffer_arrays.set_required_staging_buffer_size_to_max()
- }
  uniform_buffer_arrays.resize_staging_buffer(render_resource_context);
 
  if let Some(staging_buffer) = state.uniform_buffer_arrays.staging_buffer {