py3: Remove duplicated PyUnicode_Check() after the py3 compat macros were removed

This came about because in py2 we had to check for strings and unicode.

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Noel Power <noel.power@suse.com>

Autobuild-User(master): Noel Power <npower@samba.org>
Autobuild-Date(master): Mon Jun 24 18:48:53 UTC 2019 on sn-devel-184
