upload/editor: fix bytes/string confusion

The upload module tries to turn the strings into bytes before passing
to EditString, but it combines bytes & strings causing an error.  The
return value might be bytes or string, but the caller only expects a
string.  Lets simplify this by sticking to strings everywhere and have
EditString take care of converting to/from bytes when reading/writing
the underlying files.  This also avoids possible locale confusion when
reading the file by forcing UTF-8 everywhere.

Bug: https://crbug.com/gerrit/11929
Change-Id: I07b146170c5e8b5b0500a2c79e4213cd12140a96
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/245621
Reviewed-by: David Pursehouse <dpursehouse@collab.net>
Tested-by: Mike Frysinger <vapier@google.com>

subcmds/upload.py

@@ -271,11 +271,6 @@ Gerrit Code Review:  https://www.gerritcodereview.com/
       branches[project.name] = b
     script.append('')
 
-    script = [ x.encode('utf-8')
-             if issubclass(type(x), unicode)
-             else x
-             for x in script ]
-
     script = Editor.EditString("\n".join(script)).split("\n")
 
     project_re = re.compile(r'^#?\s*project\s*([^\s]+)/:$')