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/security/digest-sha256.t.cpp b/tests/unit-tests/security/digest-sha256.t.cpp
index 6facb98..d49b5b4 100644
--- a/tests/unit-tests/security/digest-sha256.t.cpp
+++ b/tests/unit-tests/security/digest-sha256.t.cpp
@@ -21,7 +21,7 @@
 
 #include "security/digest-sha256.hpp"
 #include "security/validator.hpp"
-#include "util/digest.hpp"
+#include "util/sha256.hpp"
 #include "util/string-helper.hpp"
 
 #include "identity-management-fixture.hpp"