Simplify torchdata version extraction in packaging script

[atalman]

Simplify torchdata version extraction in packaging script
test:

conda list -fe torchdata 
# This file may be used to create an environment using:
# $ conda create --name <env> --file <this file>
# platform: linux-64
torchdata=0.7.0.dev20230328=py310

conda list -fe torchdata | grep torchdata | sed -e 's/torchdata=\(.*\)=py.*/\1/'
0.7.0.dev202303283

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[osalpekar]

@atalman Looks like Linux Conda release jobs start failing from this PR. Nightlies were fine until 03/27 and started failing on 03/28: https://github.com/pytorch/text/actions/workflows/build-conda-linux.yml?query=event%3Apush+branch%3Anightly. We might need to revert/refactor this to get nightlies green again (looks like we are affecting the version compatibility based on the build error).

cc @joecummings