Don't use SDL2.

Index: src/common.h
--- src/common.h.orig
+++ src/common.h
@@ -20,7 +20,7 @@
 #endif
 
 // uncomment this next line if you want to disable SDL (which is for music/sound)
-//#define DONT_INCLUDE_SDL
+#define DONT_INCLUDE_SDL
 
 /* some compilers sometimes define _WIN32 but not WIN32 on Windows, but LCS usually
    just checks if WIN32's defined, so the next couple lines fix that so it works */
