Fix T91808: Batch Generate Previews fails

Caused by the Cycles-X merge.

The old style of tile rendering was removed, leaving the script to error
out trying to set the tile size.

Tile rendering came back in a new form (but only really relevant for
large resolution rendering), so now leave setting auto_tile & tile_size
alone (since previews are rendered at PREVIEW_RENDER_DEFAULT_HEIGHT 128
-- which should never make a difference here).

Maniphest Tasks: T91808

Differential Revision: https://developer.blender.org/D12937

release/scripts/modules/bl_previews_utils/bl_previews_render.py

@@ -140,8 +140,6 @@ def do_previews(do_objects, do_collections, do_scenes, do_data_intern):
         scene.render.use_overwrite = True
         scene.render.use_stamp = False
         scene.render.threads_mode = 'AUTO'
-        scene.render.tile_x = RENDER_PREVIEW_SIZE // 4
-        scene.render.tile_y = RENDER_PREVIEW_SIZE // 4
 
         image = bpy.data.images.new("TEMP_render_image", RENDER_PREVIEW_SIZE, RENDER_PREVIEW_SIZE, alpha=True)
         image.source = 'FILE'