jit/containers.h shouldn't pull in smart-containers.h

Summary: We're using std containers right now, so there's no reason to pull in
the smart ones.

Reviewed By: @edwinsmith

Differential Revision: D1579289
Move GuardConstraints to its own header

Summary: There's no reason for everyone to include it via ir.h

Reviewed By: @ottoni

Differential Revision: D1579426
Move StackValueInfo methods to simplifier.cpp

Summary: This lets us forward declare SSATmp and IRInstruction in simplifier.h
Since simplifier.cpp is the only user of StackValueInfo methods this
shouldn't change perf.

Reviewed By: @edwinsmith

Differential Revision: D1579548