common/math_util: Remove unnecessary static from PI

const/constexpr variables have internal linkage by default.

src/common/math_util.h

@@ -9,7 +9,7 @@
 
 namespace MathUtil {
 
-static constexpr float PI = 3.14159265f;
+constexpr float PI = 3.14159265f;
 
 template <class T>
 struct Rectangle {