Additional Windows fixups for Fast Kmeans

.. std::max needs <algorithm> and don't need <unistd> at all.

contrib/kmeans/hamerly_kmeans.cpp

@@ -7,6 +7,7 @@
 #include "hamerly_kmeans.h"
 #include "kmeans_general_functions.h"
 #include <cmath>
+#include <algorithm>
 
 /* Hamerly's algorithm that is a 'simplification' of Elkan's, in that it keeps
  * the following bounds:

contrib/kmeans/kmeans_general_functions.cpp

@@ -13,7 +13,6 @@
 #include <numeric>
 #include <cstring>
 #include <cstdio>
-#include <unistd.h>
 
 void addVectors(double *a, double const *b, int d) {
     double const *end = a + d;