gnss/modemmanager: Do not check for modem to be enabled

Modemmanager versions >= 1.23 allow GPS to be used also when the modem is not enabled (i.e. does not have a SIM). Remove the modem enabled check from the mm driver so that SIMless modems work with gnss-share.

Shortly tested on a SIMless Pinephone with modemmanager 1.23.4-dev, seems to work OK.