common/math_util: Remove unused IntervalsIntersect() function

This hasn't been used since the project started, so we may as well get
rid of it to keep it from bit rotting.

src/common/math_util.h

@@ -4,7 +4,6 @@
 
 #pragma once
 
-#include <algorithm>
 #include <cstdlib>
 #include <type_traits>
 
@@ -12,11 +11,6 @@ namespace MathUtil {
 
 static constexpr float PI = 3.14159265f;
 
-inline bool IntervalsIntersect(unsigned start0, unsigned length0, unsigned start1,
-                               unsigned length1) {
-    return (std::max(start0, start1) < std::min(start0 + length0, start1 + length1));
-}
-
 template <class T>
 struct Rectangle {
     T left{};