Remove unused dependency libmagic

Our use of libmagic isn't very portable, and the checks aren't used
anyway. Therefore removing dependency on libmagic.

Fixes #17.

include/linuxdeploy/util/util.h

@@ -1,5 +1,4 @@
 // local includes
-#include "magicwrapper.h"
 #include "misc.h"
 
 // import functions from misc module for convenience