Removed _USE_MATH_DEFINES directive (#596)

Since none of the `M_` prefixed constants are used anywhere in the code, this is unnecessary.  It's also Windows-specific, so these non-standard defines shouldn't be used anyway.

Ref: https://learn.microsoft.com/en-us/cpp/c-runtime-library/math-constants?view=msvc-170

RecastDemo/Source/MeshLoaderObj.cpp

@@ -20,7 +20,6 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <cstring>
-#define _USE_MATH_DEFINES
 #include <math.h>
 
 rcMeshLoaderObj::rcMeshLoaderObj() :