pstack: drop task_on_cpu() helper

This was introduced in drgn 0.0.33. For UEK it's doing nothing more than
"cpu_curr(prog, task_cpu(task)) == task". So open-code it instead. This
fixes errors like:

ImportError: cannot import name 'task_on_cpu' from 'drgn.helpers.linux' (/usr/lib64/python3.9/site-packages/drgn/helpers/linux/__init__.py)

Signed-off-by: Stephen Brennan <[email protected]>

Author: brenns10

drgn_tools/pstack.py

@@ -57,7 +57,6 @@
 from drgn.helpers.linux import for_each_online_cpu
 from drgn.helpers.linux import for_each_task
 from drgn.helpers.linux import for_each_vma
-from drgn.helpers.linux import task_on_cpu
 from drgn.helpers.linux import task_state_to_char
 from drgn.helpers.linux import vma_find
 
@@ -767,7 +766,7 @@ def pstack_print_process(task: Object) -> None:
         tcomm = thread.comm.string_().decode("utf-8", errors="replace")
         st = task_state_to_char(thread)
         cpu = task_cpu(thread)
-        on_cpu = task_on_cpu(thread)
+        on_cpu = cpu_curr(prog, cpu) == thread
         cpunote = "RUNNING ON " if on_cpu else ""
         print(f"  Thread {i} TID={tid} [{st}] {cpunote}CPU={cpu} ('{tcomm}')")
         try: