Removing research models

Removing research models.

Removing research models.

Add new import paths to mnist_tpu.py (tensorflow#4133)

* Add new import paths to mnist_tpu.py

This adds new import paths to mnist_tpu.py so individuals can check out the git repository and run `python mnist_tpu.py` without finagling with python import search paths.

* Fix lint errors

* Add disable= to pylint instructions

* Remove parent path

* Update comments

Removing research models.

Removing research models.

Removing research models

Removing research models