Remove comments about possible maintenance events during live migration (#1906)
Remove comments about possible maintenance events during live migration (#1906)

The comments do not match up with the published documentation which
states that only the MIGRATE_ON_HOST_MAINTENANCE event will ever be
published for a host to receive.
(https://cloud.google.com/compute/docs/storing-retrieving-metadata#maintenanceevents)
GoogleCloudPlatform/python-docs-samples,GoogleCloudPlatform/python-docs-samples,GoogleCloudPlatform/python-docs-samples,GoogleCloudPlatform/python-docs-samples