vndk-def: Fix `check-dep --check-apk` in Python 2

`string.decode('mutf-8')` converts `bytes` into `str` in Python 3.  On
the other hand, `string.decode('mutf-8')` converts `str` to `unicode` in
Python 2.  However, finding a `str` object in a set of `unicode`
objects may lead to false negatives.

This commit fixes the problem by encoding strings into `utf-8` after
decoding from `mutf-8`.

Bug: 110450167
Test: ./tests/run.py
Change-Id: Ifa6e97fffb5f364d0488cc98b6c59fbf4fb7869f
1 file changed