Remove shouldUseLinkRoleForPressableText feature flag (#55121)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/55121

Changelog: [Android][Fixed] - Set accessibilityRole to "link" for pressable Text components by default

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This diff removes the `shouldUseLinkRoleForPressableText` feature flag since it has been tested in FB4A for a month with `defaultValue: true`.

The flag was introduced to automatically set `accessibilityRole="link"` for pressable Text components by default. This behavior is now the default.

Changes:
- Removed the flag definition from `ReactNativeFeatureFlags.config.js`
- Removed the conditional checks in `Text.js` (2 locations), now `shouldUseLinkRole` is computed directly without the feature flag
- Removed the override from `ReactNativeFeatureFlagsOverrides_Facebook.js`
- Updated tests in `Text-test.js` to remove flag mocking and only test the enabled behavior
- Regenerated all feature flag files via `js1 featureflags --update`

Reviewed By: javache

Differential Revision: D90385104

fbshipit-source-id: 2dc0e74209e75c954445434513fbba0f7a97f7af