fix(wire-protocol): don't allow override of `slaveOk`
fix(wire-protocol): don't allow override of `slaveOk`

The wire protocol refactor accidentally allowed the `slaveOk`
bit to be set in layers above the common `command` method. This
change reverts that, and always explicitly sets the value based
on the current read preference.

mongodb/node-mongodb-native,mongodb/node-mongodb-native,mongodb/node-mongodb-native,mongodb/node-mongodb-native