device-google-gru: Update deviceinfo and maintainer

Sebastian Fleerrequested to merge
sepp/pmaports:google-gru-deviceinfo into master

Remove/replace obsolete or unnecessary variables.

disable_dhcpd doesn't make much sense to me either, but I kept it since it seems to have been explicitly enabled (but sadly without an explanation in the commit message): e7cdce22

Add myself as maintainer (see !7253 (comment 509609)).

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