Remove legacy Quake bbox expansion: CTF

Remove legacy Quake bbox expansion: CTF

This adds a feature: if the flag is dropped in a place its bbox doesn't
fit, the player's bbox (crouched or full size) is used as a fallback.
This prevents it getting stuck so physics can still move it, and it will
be expanded to full size if it's moved to a place where it does fit.

This MR adds this to flags only, because they already had half the code.
I'll add it to other big ents that players can drop (keys, balls,
powerups) in another MR.