[FIX] P3: mail: message parsing must return native strings

There was a leftover explicit conversion to bytestrings during the
parsing of HTML email parts.

This translated into a parse result with `msg_dict['body']` as a `bytes`
instance in Python 3, instead of the expected text type.

Coercing the result of etree.tostring() with UTF-8 encoding to a
native string should preserve the semantics in both Python versions
without this side-effect.

+ simplify another instance of native string use

0 files changed, 0 insertions, 0 deletions