Remove temporary hacks relating to the closure naming race

Summary: We believe this was fixed.  Leaving the assertions about unique
classes actually being unique, but we don't need to merge closure use var types
into a list of closures anymore.

Reviewed By: @ptarjan

Differential Revision: D1439704
Fix interp for VGetN

Summary: It was not popping one of its inputs.  Found in D1346023; putting up
this diff to decouple the fix from that.

Reviewed By: @alexmalyshev

Differential Revision: D1439827
Add stats in hhbbc about persistent static properties

Summary: We're going to have to redo this in hhbbc if we want to turn off
inferTypes, so I was looking at how many there are.  (Right now there's also an
issue: if you turn off inferTypes, it appears that every static property gets
marked as persistent, because isIndirectAltered defaults false everywhere, and
we'll behave horribly wrongly at runtime.)

I think it would probably be pretty trivial to do this for private statics
right now, but a huge majority of the cases of this are public statics from
thrift classes, so it's probably necessary to make something that can track
generally which statics could be assigned to.

Reviewed By: @alexmalyshev

Differential Revision: D1439901