Remove unneeded <algorithm> includes

One of these days, I need to get around to running Include What You Use
on this codebase. Until then, while I was working on #624, I noticed
these; I'm removing them now.

desktop_version/src/FileSystemUtils.cpp

@@ -1,4 +1,3 @@
-#include <algorithm>
 #include <iostream>
 #include <iterator>
 #include <physfs.h>

desktop_version/src/Graphics.h

@@ -1,7 +1,6 @@
 #ifndef GRAPHICS_H
 #define GRAPHICS_H
 
-#include <algorithm>
 #include <map>
 #include <string>
 #include <vector>

desktop_version/src/editor.cpp

@@ -3,6 +3,7 @@
 #define ED_DEFINITION
 #include "editor.h"
 
+#include <algorithm>
 #include <physfs.h>
 #include <stdio.h>
 #include <string>