Update Common.robot and requirements for correct LT variable handling

[shivanks-hue]

Pull Request: Update common.robot for LambdaTest iOS Execution
Summary
This update cleans up and simplifies the common.robot file used for Appium iOS tests.

Key Changes:

1. Replaced undefined ${version} with ${platformVersion}.
2. Updated LambdaTest Grid URL to use ${username} and ${accesskey} directly.
3. Removed unnecessary environment-based TRY/EXCEPT logic.
4. Cleaned up capability definitions and added consistent variables (e.g., devicelog=True).
5. Simplified Remote URL and APP ID handling.
6. General formatting and readability improvements.