vector_math: remove broken SFINAE stuff

this was originally added to eliminate warnings on MSVC, but it doesn't work for custom types.

src/common/vector_math.h

@@ -31,7 +31,6 @@
 #pragma once
 
 #include <cmath>
-#include <type_traits>
 
 namespace Math {
 
@@ -90,7 +89,7 @@ public:
         x -= other.x;
         y -= other.y;
     }
-    template <typename Q = T, class = typename std::enable_if<std::is_signed<Q>::value>::type>
+
     Vec2<decltype(-T{})> operator-() const {
         return MakeVec(-x, -y);
     }
@@ -247,7 +246,7 @@ public:
         y -= other.y;
         z -= other.z;
     }
-    template <typename Q = T, class = typename std::enable_if<std::is_signed<Q>::value>::type>
+
     Vec3<decltype(-T{})> operator-() const {
         return MakeVec(-x, -y, -z);
     }