Replace deprecated PyTorch Anaconda channel install instructions

[omkar-334]

Fixes #3428

Description

Both the pytorch and pytorch-nightly Anaconda channels stopped receiving updates past PyTorch 2.5 (see pytorch/pytorch#138506). This PR removes the four remaining tutorial pages that still recommend them.

Files changed

• beginner_source/introyt/tensorboardyt_tutorial.py
• recipes_source/recipes/tensorboard_with_pytorch.py
• beginner_source/introyt/captumyt.py
• advanced_source/sharding.rst

Checklist

• The issue that is being fixed is referred in the description (see above "Fixes #ISSUE_NUMBER")
• Only one issue is addressed in this pull request
• Labels from the issue that this PR is fixing are added to this pull request
• No unnecessary issues are included into this pull request.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/tutorials/3864

• 📄 Preview Python docs built from this PR

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As of commit 285923e with merge base 08435cc ():
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[omkar-334]

This includes the 3 instances mentioned in #3428 (comment), along with 1 other instance I found in the codebase

[omkar-334]

Thanks @svekars I've applied the changes from your review