How to remove silicone from brick
I'm not sure that complete removal is an option.  As a result, the way I would tackle this is as follows:

First, remove as much as possible with scraping.

Next, paint (matching the brick color).

If that still doesn't provide an acceptable asthetic, cover it up.  Contact the window manufacturer to find out what stain was used and make a trim piece of wood that will cover the gap and the residual caulk.