remove empty file mount from yaml config

[cg505]

skypilot/sky/backends/backend_utils.py

Lines 188 to 192 in b92b47f

	file_mounts = yaml_config.get('file_mounts', {})
	# Remove the file mounts added by the newline.
	if '' in file_mounts:
	assert file_mounts[''] == '', file_mounts['']
	file_mounts.pop('')

This is also present in _deterministic_yaml_hash

It's not entirely clear why this is needed, try to remove it.

ref #4289 (comment)