test: Remove boost::split from rpc_tests.cpp #25025

No need for boost, as there are no tabs.

Can be tested with:

diff --git a/src/test/rpc_tests.cpp b/src/test/rpc_tests.cpp
index 50b5078110..ad6a888ad0 100644
--- a/src/test/rpc_tests.cpp
+++ b/src/test/rpc_tests.cpp
@@ -29,6 +29,7 @@ public:
 
 UniValue RPCTestingSetup::CallRPC(std::string args)
 {
+Assert(args.find('\t')==std::string::npos);
     std::vector<std::string> vArgs;
     boost::split(vArgs, args, boost::is_any_of(" \t"));
     std::string strMethod = vArgs[0];

utACK fad35e9afdd0bb6e8d6bf7f34a31de11aeb2d39b