fix: remove incorrect warn about icon 1024x1024 size

[keiver]

This pull request updates the minimum and recommended requirements for icon images in the TvOS asset processing tool. The changes remove the recommended icon size threshold (1280x1280), making 1024x1024 both the minimum and sufficient size for all outputs. Related warnings and tests for the recommended icon size have also been removed for consistency.

Icon size requirement updates:

• The recommended icon size (1280x1280) has been removed from the documentation in README.md; 1024x1024 is now considered sufficient for all outputs.
• The ICON_RECOMMENDED constant has been removed from src/config.ts, and all references to a recommended icon size have been deleted.

Validation logic and test updates:

• The warning for icon images below the recommended size has been removed from the validation logic in src/config.ts.
• The corresponding test that checked for a warning when the icon was below the recommended size has been removed from tests/config.test.ts.
• The comment for createTestIcon in tests/fixtures/create-fixtures.ts has been updated to remove reference to the recommended minimum.

[github-actions]

Released as v1.2.1 and published to npm.