Remove pytext-nlp (#1049)

The latest version (0.3.3) was released in June 2020 and is only
compatible with Pytorch 1.5: https://github.com/facebookresearch/pytext/blob/fad9639bf733ca0d5aaf2a3a9eaca64e90675d84/requirements.txt#L19

Usage on Kaggle is very low (~2-3 sessions per day).

Author: rosbo

Dockerfile

@@ -370,11 +370,6 @@ RUN pip install flashtext && \
     pip install https://github.com/hbasria/ggpy/archive/0.11.5.zip && \
     pip install cesium && \
     pip install rgf_python && \
-    # b/185992410: onnx is a dependency of pytext, but the version 1.9.0 breaks pytext test.
-    # Remove this installation when pytext fixes the problem.
-    pip install onnx==1.8.1 && \
-    # b/145404107: latest version force specific version of numpy and torch.
-    pip install pytext-nlp==0.1.2 && \
     pip install tsfresh && \
     pip install pykalman && \
     pip install optuna && \