chore(Android): remove legacy architecture related code

[sgaczol]

Description

This PR removes all Paper-related code leftovers on Android.

Closes https://github.com/software-mansion/react-native-screens-labs/issues/1033

Changes

• remove ReactProp annotations from SearchBarManager.kt
• remove new architecture guards from build.gradle and CMakeLists.txt

Before & after - visual documentation

N/A

Test plan

Build app.

Checklist

• Ensured that CI passes

[Copilot]

Pull request overview

This PR removes all Paper/old architecture-related code from the Android configuration and implementation, completing the migration to the new React Native architecture. The project now assumes all builds use the new architecture exclusively.

Changes:

• Remove @ReactProp annotations and import from SearchBarManager that were part of the legacy prop system
• Remove all conditional new architecture guards from CMakeLists.txt, keeping only the new architecture code path
• Remove new architecture feature flag and related configuration from build.gradle, simplifying plugin application logic

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
android/src/main/java/com/swmansion/rnscreens/SearchBarManager.kt	Removed @ReactProp annotations and import; methods remain as interface implementations handled by the delegate pattern
android/CMakeLists.txt	Removed all conditional compilation guards; consolidated to new architecture code path with fbjni dependency
android/build.gradle	Removed isNewArchitectureEnabled() function and feature flag; React Gradle plugin now conditionally applied based on repo context rather than architecture flag

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