That's part of the emissions system. The idea from back in the 60's is that you don't want to vent gas fumes (aka pollution) to the atmosphere through a vented gas cap, so an evaporative emissions system was designed. It utilizes a gas cap that won't vent TO the atmosphere, but will allow air IN (one-way valve) if the tank needs it due to a vacuum condition. Instead of venting externally, the fumes are pushed through the vent line up to the cannister. From there, they get pulled into the intake and burned along with the regular air/fuel mix.
If you leave it sitting open like that you're polluting (yeah, yeah; big deal) but more importantly you have an open fuel vapor source hanging around under your hood which isn't exactly safe. Sure; plenty of people have left theirs this way including people that pulled the cannister because the truck is bagged and there's no room for it, or whatever, but it's still not safe.
If you're dead set on removing it you should plug the vent line from the tank and cap the port on the TBI, problem is, to do this "right" you'd need an old-school vented cap, which could be tricky to find for a modern screw-type filler neck. If the cap can't vent externally, you'll build up pressure inside the tank and that's not good.
Honestly, my suggestion? Find some other place to mount the cannister, and repair the broken line with some vapor-rated vacuum line.
Richard
