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/ims/in-memory-storage.t.cpp b/tests/unit-tests/ims/in-memory-storage.t.cpp
index 691321a..41082c6 100644
--- a/tests/unit-tests/ims/in-memory-storage.t.cpp
+++ b/tests/unit-tests/ims/in-memory-storage.t.cpp
@@ -25,7 +25,7 @@
 #include "ims/in-memory-storage-lru.hpp"
 #include "ims/in-memory-storage-persistent.hpp"
 #include "security/signature-sha256-with-rsa.hpp"
-#include "util/digest.hpp"
+#include "util/sha256.hpp"
 
 #include "boost-test.hpp"
 #include "../make-interest-data.hpp"