refactor: remove legacy example app

[nickolas-dimitrakas]

Background

• The SDK already uses Scene Graph architecture internally, and Roku has standardized on Scene Graph for years. The legacy example adds unnecessary maintenance overhead and can confuse developers about the recommended approach.

What Has Changed

• Removed example-legacy-sdk/ directory
• Simplified deploy-and-test.sh to only support Scene Graph example
• Updated README.md to remove legacy example references

Checklist

• I have performed a self-review of my own code.
• I have made corresponding changes to the documentation.
• I have added tests that prove my fix is effective or that my feature works.
• I have tested this locally.

Additional Notes

• This PR needs to be rebased after feat: media content time spent calculation #44 gets merged to main.

Reference Issue (For employees only. Ignore if you are an outside contributor)

• Closes https://rokt.atlassian.net/browse/SDKE-778

[jamesnrokt]

Approved pending changing the base branch and merging of #44