Remove redundant includes. Conform to header include guidelines.

From the header include guidelines (developer-notes.md):

"One exception is that a `.cpp` file does not need to re-include the
 includes already included in its corresponding `.h` file."

* rpc/util.h includes pubkey.h + utilstrencodings.h. rpc/util.cpp includes rpc/util.h.
* util.h includes fs.h. util.cpp includes util.h.

src/rpc/util.cpp

@@ -4,7 +4,6 @@
 
 #include <base58.h>
 #include <keystore.h>
-#include <pubkey.h>
 #include <rpc/protocol.h>
 #include <rpc/util.h>
 #include <tinyformat.h>