Reduces headers needed for external includes

hei_main.hpp included hei_isolator.hpp, which requires nearly all
headers in this project to be exported when building a library.

Change-Id: I6013ab53a7ee2b4993526bc4c62b30e8bf5f6702
Signed-off-by: Zane Shelley <zshelle@us.ibm.com>
diff --git a/src/hei_user_interface.hpp b/src/hei_user_interface.hpp
index e8740f3..d880ef4 100644
--- a/src/hei_user_interface.hpp
+++ b/src/hei_user_interface.hpp
@@ -43,7 +43,9 @@
  *  }
  */
 
-#include <hei_includes.hpp>
+#include <stdlib.h>
+
+#include <hei_chip.hpp>
 
 namespace libhei
 {