refactor: drop protocol.h include header in rpc/util.h

as it was only needed for GetServicesNames(). This potentially avoids needlessly
compiling the 500 lines of protocol.h in the 35 files other than rpc/net.cpp
that include rpc/util.h.

Drop an unneeded CPubKey forward declaration. The other IWYU suggestions would
require more extensive changes in other files.

Add 3 already-missing include headers in other translation units that are needed
to compile without protocol.h in rpc/util.h, as it includes netaddress.h, which
in turn includes util/strencodings.h.

src/rpc/util.h

@@ -9,7 +9,6 @@
 #include <consensus/amount.h>
 #include <node/transaction.h>
 #include <outputtype.h>
-#include <protocol.h>
 #include <pubkey.h>
 #include <rpc/protocol.h>
 #include <rpc/request.h>
@@ -59,7 +58,6 @@ extern const std::string UNIX_EPOCH_TIME;
 extern const std::string EXAMPLE_ADDRESS[2];
 
 class FillableSigningProvider;
-class CPubKey;
 class CScript;
 struct Sections;