Where did you find this file?
I have the problematic “distributor” mqtt in services on Paper UI as well and want to get rid of it.
My cfg files are in /etc/openhab2/services, but there is no mqtt.cfg or similar.
When OH is running these .cfg files are usually copied to /srv/openhab2-userdata/config/org/openhab/ with extension .config (AFAIK).
None of these exist.
I just found these:
mqttembeddedbroker.config
mqttbroker.config
According to David above (sorry if I got you wrong, @David, because there are too many mqtts involved 
the first one should be the config which is about the internal (embedded) mqtt broker of OH (I intend using mosquitto instead), the second is the “distributors only” which can be found in PaperUI → configuration → services (I guess!?)
EDIT:
After deleting the two files above (after shutting down OH), no negative effect is obvious.
AND: I don’t get the mqtt stuff being discovered anymore (was very annoying).