Remove useless const qualifiers from returns

Remove const qualifiers applied to POD return values, as these are
meaningless and ignored by the compiler and are therefore potentially
misleading. (They also trip -Wignored-qualifiers.)

src/BulletInverseDynamics/details/IDLinearMathInterface.hpp

@@ -22,7 +22,7 @@ public:
 	vec3(const btVector3& btv) { *this = btv; }
 	idScalar& operator()(int i) { return (*this)[i]; }
 	const idScalar& operator()(int i) const { return (*this)[i]; }
-	const int size() const { return 3; }
+	int size() const { return 3; }
 	const vec3& operator=(const btVector3& rhs) {
 		*static_cast<btVector3*>(this) = rhs;
 		return *this;