get rid of flask tutorials

[msaroufim]

There were a lot of old flask tutorials

pt ❯ grep -r "flask" . 
./.ci/docker/requirements.txt:flask
./_templates/layout.html:    var div = '<div class="admonition note"><p class="admonition-title">Note</p><p><i class="fa fa-flask" aria-hidden="true">&nbsp</i> This tutorial describes a prototype feature. Prototype features are typically not available as part of binary distributions like PyPI or Conda, except sometimes behind run-time flags, and are at an early stage for feedback and testing.</p></div>'
./.devcontainer/requirements.txt:flask
./beginner_source/introyt/captumyt.py:    conda install pytorch torchvision captum flask-compress matplotlib=3.3.4 -c pytorch

✦ ~/Dev/tutorials msaroufim/delete_flask
pt ❯ 

In particular these are not needed in PyTorch since the average LLM can code generate any of this code and it's not really how modern serving is done these days

[pytorch-bot]

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[janeyx99]

lgtm other than the github workflows change