Remove redundant use material3

[2shrestha22]

Description of what this PR is changing or adding, and why:
This PR removes redundant useMaterial3 since it is true by default.

Issues fixed by this PR (if any):
flutter/flutter#162818

PRs or commits this PR depends on (if any):

Presubmit checklist

• This PR is marked as draft with an explanation if not meant to land until a future stable release.
• This PR doesn’t contain automatically generated corrections (Grammarly or similar).
• This PR follows the Google Developer Documentation Style Guidelines — for example, it doesn’t use i.e. or e.g., and it avoids I and we (first person).
• This PR uses semantic line breaks of 80 characters or fewer.

[sfshaza2]

This is definitely true, but waiting for build to finish to make sure that the code excerpts are up to date.

[sfshaza2]

As I suspected. @2shrestha22, can you refresh the code excerpts on your build and re-submit the changes. It's described in the failed results of the test pass:

Error: Some code excerpts needed to be updated!
  Run `./dash_site refresh-excerpts` to update.

[parlough]

I went ahead and ran the command to update the copies of the excerpts for you.

Thanks so much for updating these snippets!

[flutter-website-bot]

Visit the preview URL for this PR (updated for commit bc64ff6):

https://flutter-docs-prod--pr11693-remove-redundant-usemateria-92n256je.web.app