gdbserver: remove unused for loop

In this commit,

  commit cf6c1e710ee162a5adb0ae47acb731f2bfecc956
  Date:   Mon Jul 11 20:53:48 2022 +0800

    gdbserver: remove unused variable

I removed an unused variable in handle_v_run.  Pedro then pointed out
that the for loop after it was also unused.  After a period of smoke
testing, no exceptions were found.

Tested on x86_64-linux.