Clean up UI tests infrastructure (#25673)

* Remove unused UI-test launch-argument flags

UI tests were removed in #25399. This drops the launch-argument flags that nothing passes anymore (logging, prompts, migration, autofill, animations, mock data, screenshot generation) along with their app-side conditionals, reducing UITestConfigurator to the simulator sign-in reset path. The sign-in launch arguments are unaffected.

* Remove screenshot-generation UI-test targets and lanes

The WordPress and Jetpack screenshot-generation targets are XCUITest targets that relied on the now-removed UI-test infrastructure. This deletes the targets, their schemes and sources, and the fastlane raw-screenshot lanes, while keeping the promo-screenshot composition and GlotPress download lanes.

* Remove UITestsFoundation package and ScreenObject dependency

With the screenshot-generation targets gone, nothing consumes the UITestsFoundation module or its XcodeTarget wrappers. This removes them and the ScreenObject package dependency they pulled in.

* Remove WireMock API mocks and UI-test CI plumbing

The WireMock mock server, its rake task, the Buildkite UI-test runner, and the Jetpack UI-test branch of the test_without_building lane only supported the removed UI tests. This deletes them along with the obsolete UI-tests documentation.

Author: crazytonyli