util: rename digest.hpp to sha256.hpp

The new file name matches the Sha256 class included within.

This commit also deletes deprecated crypto.hpp.

refs #3940

Change-Id: Ib9bbcd0ba087b812bb0886ceaea116689d4633f5
diff --git a/tests/unit-tests/exclude.t.cpp b/tests/unit-tests/exclude.t.cpp
index a6823c6..715f747 100644
--- a/tests/unit-tests/exclude.t.cpp
+++ b/tests/unit-tests/exclude.t.cpp
@@ -20,7 +20,7 @@
  */
 
 #include "exclude.hpp"
-#include "util/digest.hpp"
+#include "util/sha256.hpp"
 
 #include "boost-test.hpp"