Do not set "mongodb.debug" based on Manager's $driverOptions["debug"]

php_phongo_make_mongo_client() currently sets mongodb.debug based on $driverOptions["debug"]. This is problematic, since the INI option is global and could affect multiple Manager instances. This behavior was never documented, so we should simply remove it.

In the future, we can look into re-introducing such an option if we can limit its scope to a single Manager instance.