Remove some unnecessary checks for None

[rwbarton]

I find extraneous checks of this kind confusing; suggesting that None is expected as a possible value when in fact it has no meaning and is (or is expected to be) impossible.

[gvanrossum]

Did you check the history of those lines? They look like the kind of things that might have been put in to avoid a crash.

[rwbarton]

I know that the TypeVarType one really could have been None until b602ecc, and the check for None is much older than that (42b9328 which also added a test that reproduced the crash).

The is_generic one is unchanged from 2012 when this file was written in the mypy language; there doesn't seem to have ever been a version of this line without the None check, so I think either it was redundant from the start, or there were surrounding changes that made it redundant (I have some uncertainty due to not knowing the runtime semantics of the old mypy language!)

[gvanrossum]

The first comes from 42b9328 (fixes #674) and I worry that you might be reintroducing the bug.

The second comes from d3872f9 and it looks like you're doing the right thing there.

[gvanrossum]

OK, our messages crossed. I see your point. Merging.