clean: Remove experimental cheat auto-population code from S-Pen branch

This commit cleans up the S-Pen implementation branch by removing experimental
cheat auto-population functionality that was accidentally mixed in during
development. The cheat code was causing cross-platform build failures when
non-Android platforms tried to compile Android-specific APIs.

The core S-Pen functionality remains intact and working:
- S-Pen input properly maps to RETRO_DEVICE_POINTER for libretro compatibility
- Stylus tool type detection (AMOTION_EVENT_TOOL_TYPE_STYLUS)
- Phantom touch prevention through proximity detection
- Side button (barrel) functionality
- Contact-based clicking behavior
- Proper #ifdef ANDROID guards for platform-specific code

Sorry for the confusion - this branch now contains only the clean S-Pen
implementation ready for upstream submission.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: f4mrfaux