FastSpeech2_HiFiGAN_E2E training doesn't work
**Describe the bug**

The class for training FastSpeech2_HiFiGAN end-to-end model uses variables that aren't present in the core NeMo classes, so the python errors out before training begins.

**Steps/Code to reproduce bug**

Try training such a model using NeMo 1.5.1

**Expected behavior**

A model can be trained
