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/editor.cpp

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