Revert "Support formatting python3 scripts"

This reverts commit 2ba05f16.

Reason for revert: yapf formatting broken on windows  https://crbug.com/1095581

Change-Id: Ifad1009ab8d83a05cd5763bb95910647940cbaf1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2246152
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>

git_cl.py

@@ -4931,13 +4931,7 @@ def CMDformat(parser, args):
       if not yapf_style:
         yapf_style = 'pep8'
 
-      with open(f, 'r') as py_f:
-        if 'python3' in py_f.readline():
-          vpython_script = 'vpython3'
-        else:
-          vpython_script = 'vpython'
-
-      cmd = [vpython_script, yapf_tool, '--style', yapf_style, f]
+      cmd = [yapf_tool, '--style', yapf_style, f]
 
       has_formattable_lines = False
       if not opts.full: