What should I do with the extra wire when intalling a new remote for my ceiling fan?
The "Common Out" lead on the old receiver module, is simply a grounded (neutral) conductor. Since the new receiver doesn't have this lead. You'll want to connect the white wire from the fixture, together with the white wire from the ceiling, and the white (neutral in) wire from the new receiver. 

The new wiring should be connected as follows:


Ungrounded (hot) conductor from ceiling to Live In wire on receiver.
Grounded (neutral) conductor from ceiling to 'Neutral Inon receiver, andCommon` from fixture.
Light Out on receiver to light (blue) wire on fixture.
'Fan Out` on receiver to fan (black) wire on fixture.
All grounding (green, bare, etc.) conductors should be connected together, and connected to the ceiling box if it's a metal box.


Notes: I've tried to keep the answer applicable to all areas, however, wire colors used in this answer are for the US and may be different in other countries.