remove the following code in arguments.cpp

    // -Xconcgc
    } else if (match_option(option, "-Xconcgc")) {
      warning("-Xconcgc uses UseConcMarkSweepGC; support was removed for both options in 14.0");
    // -Xnoconcgc
    } else if (match_option(option, "-Xnoconcgc")) {
      warning("-Xnoconcgc uses UseConcMarkSweepGC; support was removed for both options in 14.0");