[ET-VK] Don't specify memory layouts when testing (#7324)

As title. Now that we have a memory metadata tagging pass that automatically determines the optimal memory layout to use for operators, there is no need to specify what memory layout to test in the Python export tests.

There were some issues with the memory metadata tagging pass when dealing with nodes that contain tensor lists, which have been fixed as part of this diff as well.

Differential Revision: [D67180897](https://our.internmc.facebook.com/intern/diff/D67180897/)

ghstack-source-id: 258028337
Pull Request resolved: https://github.com/pytorch/executorch/pull/7322

Co-authored-by: Stephen Jia <ssjia@meta.com>