Remove Default WC Majority 4.4 upgrade tests once we branch 5.0

Remove these tests since we don't need them in the main branch after we have a separate 5.0 branch
since all 4.4 upgrades have to go to a 5.0 binary version first:

• upgrade_with_non_default_get_last_error_defaults_fails_on_startup.js
• migrate_from_get_last_error_defaults_to_cluster_wide_write_concern.js