Remove it. Any branch that is the same size/diameter as the central leader/trunk will turn into a giant fork in the tree. And you won't be able to remove it years later without taking half of the trees crown with it. Removing it will also stimulate other branches to develop.

This is the outcome. I was careful to not cut into the branch collar so that it will heal correctly. It's not a very full tree now, not that it was before either really, but hopefully it's worth it. I also learned through various sources to prune maples in the summer when it's not too hot. I always thought pruning was supposed to be done in the winter. Learn something everyday.

Ah... A much nicer tree now. I cringe when I drive through my neighborhood and see poorly-pruned or neglected trees. Don't forget to put trunk protection on later for the winter. (But you probably already know that.)

Yes, I plan on some corrugated plastic tubing to keep rodents at bay probably at the end of September or so right before it starts getting cold at night.