Revert "[tools] Add a simple gdb frame unwinder"

This reverts commit c3ac338b.

Reason for revert: Breaks stepping with `n`

Original change's description:
> [tools] Add a simple gdb frame unwinder
>
> Add a simple unwinder for gdb which, on x64,  walks frame pointers
> whenever there is no source information available. Ideally we would only
> do this for V8 PCs but this appears hard to do in an Unwinder without
> messing with gdb's internal assumptions.
>
> Change-Id: Iba1e62a3768340ee912e81d691237c1920a8ae91
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3608628
> Reviewed-by: Camillo Bruni <cbruni@chromium.org>
> Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#80204}

Change-Id: I0264cf34cfe8fe2331bacf202dedbb4706535936
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3644855
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Auto-Submit: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80493}

tools/gdbinit

@@ -259,55 +259,3 @@ gdb.events.new_objfile.connect(newobj_handler)
 gdb.execute("set environment V8_GDBINIT_SOURCED=1")
 
 end
-
-# Add a simple unwinder which, on x64, walks frame pointers when there
-# is no source information available.
-python
-
-from gdb.unwinder import Unwinder
-
-class V8UnwinderFrameId(object):
-  def __init__(self, sp, pc):
-    self.sp = sp
-    self.pc = pc
-
-class V8Unwinder(Unwinder):
-  def __init__(self):
-    super(V8Unwinder, self).__init__("V8Unwinder")
-    self.enabled = True
-
-  def __call__(self, pending_frame):
-    try:
-      # Only supported on x64.
-      if gdb.selected_inferior().architecture().name() != "i386:x86-64":
-        return None
-
-      pc = pending_frame.read_register("rip")
-      sym_and_line = gdb.current_progspace().find_pc_line(int(pc))
-
-      if sym_and_line.symtab is not None:
-        return None
-      fp = pending_frame.read_register("rbp").reinterpret_cast(
-          gdb.lookup_type("void").pointer().pointer())
-
-      next_sp = fp
-      next_fp = fp.dereference()
-      next_pc = (fp+1).dereference()
-
-      frame_info = V8UnwinderFrameId(next_sp, next_pc)
-
-      # create_unwind_info seems to sometimes have issues accessing
-      # the frame_info if it's not first accessed in Python.
-      _lol_gdb_workaround = frame_info.pc + 1
-
-      unwind_info = pending_frame.create_unwind_info(frame_info)
-      unwind_info.add_saved_register("rsp", next_sp)
-      unwind_info.add_saved_register("rip", next_pc)
-      unwind_info.add_saved_register("rbp", next_fp)
-      return unwind_info
-    except Exception as e:
-      return None
-
-gdb.unwinder.register_unwinder(None, V8Unwinder(), replace=True)
-
-end