UWP: Remove platform port, needs to be redone from scratch for 4.x

The UWP platform port was never ported to the Godot 4.0+ API,
and it's now accumulating bitrot as it doesn't compile, and thus
we no longer propagate platform changes in it.

So we finally remove to acknowledge this state. There's still some
interest in reviving the UWP port eventually, especially as support
for Direct3D 12 will soon be merged, but when that happens it will
be easiest to redo it from scratch.

core/input/input_builders.py

@@ -51,7 +51,6 @@ def make_default_controller_mappings(target, source, env):
         "Android": "#if defined(__ANDROID__)",
         "iOS": "#ifdef IOS_ENABLED",
         "Web": "#ifdef WEB_ENABLED",
-        "UWP": "#ifdef UWP_ENABLED",
     }
 
     g.write("const char* DefaultControllerMappings::mappings[] = {\n")