What would happen if an airliner had too much fuel for its next flight?
This would be an uncommon situation and the decision on what to do will typically be handled by your dispatcher.


Take the extra gas and restrict passenger/cargo weight as necessary.

This is the easy option but it could mean leaving people behind.
Defuel to the normal amount of fuel needed (e.g. release + taxi + contingency fuel) 

This normally means the fuel is considered contaminated and will be disposed of.  There are ways of de-fuelling and re-using that fuel for another plane, but it requires specific operations and equipment that only likely to be available in the hub or perhaps a maintenance station.  De-fuelling can be slow and will delay the flight.


In the end this comes down to either weight restricting the plane or taking a delay and wasting some fuel.  The timing and economics of the decision will depend on many factors and each case would be judged individually.