Cleanup/remove wii port

[DCurrent]

Removes the legacy Wii port from OpenBOR.

This cleanup removes Wii-specific backend files, build wiring, SDK/toolchain references, IDE project entries, documentation references, and remaining source-level Wii conditionals. The supported platform focus is now Windows, Android, and Linux.

Changes

• Removed Wii build targets from CMake, legacy Makefile, and shell build scripts
• Removed DevkitPro / devkitPPC / libogc tooling references
• Removed bundled Wii SDK artifact handling
• Removed Wii source references from Visual Studio and CodeBlocks project files
• Removed Wii-specific runtime, video, input, threading, type, PNG, RAM, and utility branches
• Updated compiling documentation and README platform/history messaging
• Left historical README contributor mentions intact

Validation

• Confirmed the project compiles after cleanup
• Verified no remaining Wii support references outside intentional README history