[IR] Rubyclass stack fix: Quick cleanup of stale code from earlier expts.
[IR] Massive simplification of the rubyclass algo.

* I had a bug with setting inModuleEval/inInstanceEval flags.

  I was setting the flag on the parent-scope that initiated the
  module/instance eval instead of on the block that was executing
  in the context of module/instance eval.

* With this, I can walk lexical scope hierarchy and these flags
  to determine method container.
[IR] Non-hacky setting of eval flags.

* This can be fixed some more later.
* But, now all tests are green, green, green.
* The algo is also quite clean and simple now.
[IR] Cleaned up dead code in IR instrs that require method container

* Alias, DefineInstanceMethod, UndefMethod instructions no longer
  require additional fields added earlier.