Misleading comment that networked entityState_t weapon bits must be at least 8

[zturtleman]

The commit ed75b3ce3 adds a comment "// because 'weapon' is used for things besides weaponnum it must be minimum of 8 bits" however I don't see entityState_t weapon being used for anything besides weaponnum.

I may of mis-remembered weapon as being used for other things like modelindex, modelindex2, and probably some other fields are and I didn't want to reduce weapon to less than 8 bits.

I won't be changing the code at this point—to drop the hard coded 8 bit minimum to WEAPONNUM_BITS (4)—as it would needlessly break network compatibility. (Technically, I think it's possible to support multiple netfields based on CS_GAME_PROTOCOL but this isn't worth it.)

Reported by gbbofh on Discord.