How can I replace an integrated security light with a solar powered version?
Typically an exterior light will have a cable directly from the switch to the light soley for the purpose of switching. This is unlike some electrical boxes you will find in your interior where there are circuits branching off within the box, or where power might come in at the ceiling and then a cable is run to the switch.

Assuming this is the case, once you disconnect it the old switch and light, connect the hot and neutral (black/white) together with a wirenut on both ends. This is a good way of indiciating that it is no longer in use, and if someone were to mistakenly connect it again, it would short out and trip the breaker.  If it is not wired in this manner you will need to be a bit more careful with what you disconnect and tie together.

On the outside, if your new light fixture is not being mounted to the same electrical box then you would want to cap the box with a weather tight cover.