refactor: Avoid using IsArgSet() on -signetseednode and -signetchallenge list options

This commit does not change behavior because negation of -signetseednode and
-signetchallenge parameters has been disallowed since these were introduced in
#18267, so calling IsArgSet() is equivalent to checking if GetArgs() returns a
non-empty list.

Author: ryanofsky

src/chainparams.cpp

@@ -25,10 +25,10 @@ using util::SplitString;
 
 void ReadSigNetArgs(const ArgsManager& args, CChainParams::SigNetOptions& options)
 {
-    if (args.IsArgSet("-signetseednode")) {
+    if (!args.GetArgs("-signetseednode").empty()) {
         options.seeds.emplace(args.GetArgs("-signetseednode"));
     }
-    if (args.IsArgSet("-signetchallenge")) {
+    if (!args.GetArgs("-signetchallenge").empty()) {
         const auto signet_challenge = args.GetArgs("-signetchallenge");
         if (signet_challenge.size() != 1) {
             throw std::runtime_error("-signetchallenge cannot be multiple values.");