Update custom scene viewer tutorial

[iche033]

🦟 Bug fix

Summary

Following up on #893, this PR removes more references to optix in the custom scene viewer tutorial

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #895 (6a20373) into gz-rendering8 (2901ec2) will not change coverage.
The diff coverage is n/a.

❗ Current head 6a20373 differs from pull request most recent head b2d43dd. Consider uploading reports for the commit b2d43dd to get more accurate results

@@              Coverage Diff               @@
##           gz-rendering8     #895   +/-   ##
==============================================
  Coverage          75.15%   75.15%           
==============================================
  Files                176      176           
  Lines              16851    16851           
==============================================
  Hits               12664    12664           
  Misses              4187     4187