Fixed some Spawn Icons in the giveweapons module

... Again.

Didn't I already do this? Falco, silkicons are now built into GMOD. The
evidence is in my old SRCDS folder.

And vgui/achievements/ep1_beat_game_onebullet is no longer in GMOD for
clients. We cant FastDL it as thats copyright issues as previously
discussed, so we need to use a different image. The ammobox works fine
for now, until someone feels like finding something better.

For everyone else, this removes missing textures from spawn icons in the "Give Weapon" menu in fadmin.,, or atleast, it removes some missing textures such as admin only icons and ammo. Still thinking about finding an "Unknown weapon" icon.