Unpin nltk (#1530)

Also removed `preprocessing` python package because it pins `nltk`:
https://github.com/SpotlightData/preprocessing/blob/180c6472bc2642afbd7a1ece08d0b0d14968a708/requirements.txt#L1

The `preprocessing` package is unmaintained, last release was in 2017.

http://b/408298750

Author: rosbo

Dockerfile.tmpl

@@ -70,10 +70,6 @@ ADD patches/keras_internal.py \
 RUN apt-get install -y libfreetype6-dev && \
     apt-get install -y libglib2.0-0 libxext6 libsm6 libxrender1 libfontconfig1 --fix-missing
 
-# NLTK Project datasets
-# b/408298750: We currently reinstall the package, because we get the following error:
-# `AttributeError: module 'inspect' has no attribute 'formatargspec'. Did you mean: 'formatargvalues'?`
-RUN uv pip install --system --force-reinstall "nltk>=3.9.1"
 RUN mkdir -p /usr/share/nltk_data && \
     # NLTK Downloader no longer continues smoothly after an error, so we explicitly list
     # the corpuses that work

kaggle_requirements.txt

@@ -89,7 +89,6 @@ path
 path.py
 pdf2image
 plotly-express
-preprocessing
 pudb
 pyLDAvis
 pycryptodome