Inline md_wrap.c in md.c

md_wrap.c doesn't expose any public functionality and doesn't
need to be present as a separate compilation unit.
diff --git a/library/md.c b/library/md.c
index 3bb4baf..e1d7e9d 100644
--- a/library/md.c
+++ b/library/md.c
@@ -49,6 +49,8 @@
 #include <stdio.h>
 #endif
 
+#include "md_wrap.c"
+
 /*
  * Reminder: update profiles in x509_crt.c when adding a new hash!
  */