Move selinux dependencies out of header files.

Bug: http://b/27764900
Change-Id: Ib62a59edcb13054f40f514c404d32b87b14ed5f1
diff --git a/minzip/Zip.h b/minzip/Zip.h
index e6b19e1..c932c11 100644
--- a/minzip/Zip.h
+++ b/minzip/Zip.h
@@ -18,8 +18,7 @@
 extern "C" {
 #endif
 
-#include <selinux/selinux.h>
-#include <selinux/label.h>
+struct selabel_handle;
 
 /*
  * One entry in the Zip archive.  Treat this as opaque -- use accessors below.