Remove fixed resolution and set it based on the current display mode.

[christianhaitian]

Thank you for your contribution to the Fake-08 Before submitting this PR, please make sure:

• [ ] This pull request is for a single Feature or BugFix
• [ ] Your code builds clean without any errors on all platforms
• [ ] You have added unit tests (if this is a change to the core Pico 8 emulator)