scripted-diff: stop using the gArgs wrappers

They were temporary additions to ease the transition.

-BEGIN VERIFY SCRIPT-
find src/ -name "*.cpp" ! -wholename "src/util.h" ! -wholename "src/util.cpp" | xargs perl -i -pe 's/(?<!\.)(ParseParameters|ReadConfigFile|IsArgSet|(Soft|Force)?(Get|Set)(|Bool|)Arg(s)?)\(/gArgs.\1(/g'
-END VERIFY SCRIPT-

src/httprpc.cpp

@@ -210,7 +210,7 @@ static bool HTTPReq_JSONRPC(HTTPRequest* req, const std::string &)
 
 static bool InitRPCAuthentication()
 {
-    if (GetArg("-rpcpassword", "") == "")
+    if (gArgs.GetArg("-rpcpassword", "") == "")
     {
         LogPrintf("No rpcpassword set - using random cookie authentication\n");
         if (!GenerateAuthCookie(&strRPCUserColonPass)) {
@@ -221,7 +221,7 @@ static bool InitRPCAuthentication()
         }
     } else {
         LogPrintf("Config options rpcuser and rpcpassword will soon be deprecated. Locally-run instances may remove rpcuser to use cookie-based auth, or may be replaced with rpcauth. Please see share/rpcuser for rpcauth auth generation.\n");
-        strRPCUserColonPass = GetArg("-rpcuser", "") + ":" + GetArg("-rpcpassword", "");
+        strRPCUserColonPass = gArgs.GetArg("-rpcuser", "") + ":" + gArgs.GetArg("-rpcpassword", "");
     }
     return true;
 }