Revert "Specify encoding for AUTHORS file"

This reverts commit 68324eff.

Reason for revert: I think we need to revert this, because if someone tries to upload a CL from a revision older than when we switched to Python3, this'll run under Python2, where that parameter isn't accepted.

Sorry, I didn't think that part through.

Original change's description:
> Specify encoding for AUTHORS file
>
> Needed to resolve "UnicodeDecodeError" for Python 3 presubmit checks.
>
> Bug: 1210746
> Change-Id: If55190ffc9f99c671a84fe9b3539317e464639cc
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2904927
> Commit-Queue: Dirk Pranke <dpranke@google.com>
> Auto-Submit: Alan Screen <awscreen@chromium.org>
> Reviewed-by: Dirk Pranke <dpranke@google.com>

Bug: 1210746
Change-Id: I4e5a58869baa897066f4e84c2e18b673c25bcc34
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2906499
Auto-Submit: Dirk Pranke <dpranke@google.com>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>

presubmit_canned_checks.py

@@ -128,7 +128,7 @@ def CheckAuthorizedAuthor(input_api, output_api, bot_allowlist=None):
       input_api.PresubmitLocalPath(), 'AUTHORS')
   valid_authors = (
       input_api.re.match(r'[^#]+\s+\<(.+?)\>\s*$', line)
-      for line in open(authors_path, encoding="utf-8"))
+      for line in open(authors_path))
   valid_authors = [item.group(1).lower() for item in valid_authors if item]
   if not any(input_api.fnmatch.fnmatch(author.lower(), valid)
              for valid in valid_authors):