maths: remove gcd in favour of the std implementation

maths.hpp

@@ -416,25 +416,6 @@ namespace util {
     ///////////////////////////////////////////////////////////////////////////////
     // factorisation
     template <typename T>
-    constexpr T
-    gcd (T a, T b)
-    {
-        assert (a);
-        assert (b);
-
-        while (a != b) {
-            if (a > b)
-                a -= b;
-            else if (b > a)
-                b -= a;
-        }
-
-        return a;
-    }
-
-
-    //-----------------------------------------------------------------------------
-    template <typename T>
     const T&
     identity (const T& t)
     {

rand/lcg.cpp

@@ -28,7 +28,7 @@ bool is_coprime (T M, T C)
 {
     if (M == 0)
         return true;
-    if (util::gcd (M, C) == 1u)
+    if (std::gcd (M, C) == 1u)
         return true;
     return false;
 }

rational.cpp

@@ -109,7 +109,7 @@ template <typename T>
 rational<T>
 rational<T>::reduced (void) const
 {
-    auto x = gcd (abs (n), abs (d));
+    auto x = std::gcd (abs (n), abs (d));
 
     return { n / x, d / x };
 }