swift234

remove a bunch of code that is manually monkeying around with DeclContexts,
now that they are implicitly updated.  This exposes two things:
1) we're unncessarily serializing selfdecls in ctors and dtors.
2) The index pattern of a SubscriptDecl has no sensible DeclContext that 
   owns variables in it.

I'll deal with the first tomorrow, I'm not sure what to do with
the second one.


Swift SVN r13703