Hint / skip brush logic error

[jdolan]

https://github.com/ericwa/ericw-tools/blob/6f99f469c6c2b3bdddc88d89368cabb1a7054ec8/qbsp3/map.cc#L641

This line toggles the detail bit on the surface flags, not the contents flags. And the contents flags were cleared in the line above, so really, this line should just be removed.