test: remove unneeded assert on vm.state

`vm.start()` already asserts `vm.state == "Running"`, so no need to do
it again at the callsite.

Signed-off-by: Patrick Roy <roypat@amazon.co.uk>

tools/create_snapshot_artifact/main.py

@@ -120,8 +120,6 @@ def main():
                 )
 
                 vm.start()
-                # Ensure the microVM has started.
-                assert vm.state == "Running"
 
                 # Populate MMDS.
                 data_store = {