Remove dummy PRIszX macros for formatting

Size specifiers are no longer needed now that we use typesafe tinyformat
for string formatting, instead of the system's sprintf.

No functional changes.

This continues the work in #3735.

src/rpcprotocol.cpp

@@ -92,7 +92,7 @@ string HTTPReply(int nStatus, const string& strMsg, bool keepalive)
             "HTTP/1.1 %d %s\r\n"
             "Date: %s\r\n"
             "Connection: %s\r\n"
-            "Content-Length: %"PRIszu"\r\n"
+            "Content-Length: %u\r\n"
             "Content-Type: application/json\r\n"
             "Server: bitcoin-json-rpc/%s\r\n"
             "\r\n"