PLAYRTS-5538 Update RTS AppStore screenshots workflow

[pyby]

Description

Like SRF marketing team, RTS marketing takes care of the AppStore detail page, and its previews and screenshots. In the fastlane scripts, remove the "upload" step, to avoid erasing the current screenshots.

Changes Made

• Fix iOS and tvOS screenshots builds.
• Remove upload_screenshots(platform) for RTS screenshots lanes.

How to test

• Running in Xcode the screenshots targets have a build success.
• Running locally in Terminal.app creates the expected screenshots images from the target in the repository folderfastlane/export` but not upload anymore on AppStore Connect the new screenshots:
  • bundle exec fastlane iOS tvOSrtsScreenshots for RTS tvOS screenshots.
  • bundle exec fastlane iOS iOSrtsScreenshots for RTS iOS screenshots.

⚠️ Running SRF variants also don't upload new screenshots. But running RSI or RTR variants will replace on the AppStore Connect existing screenshots with new one.

Checklist

• [x] I have followed the project's style guidelines.
• [x] I have performed a self-review of my own changes.
• [x] I have made corresponding changes to the documentation.
• [x] My changes do not generate new warnings.
• [x] I have tested my changes and I am confident that it works as expected and doesn't introduce any known regressions.
• [x] I have reviewed the contribution guidelines.