[IMPROV] Use str.decode instead of unicode

With Python 3 unicode was removed. To support both versions 'unicode' is
aliased as 'str' in Python 3. But the usage of 'unicode(str, enc)' is
not necessary and instead 'str.decode(enc)' can be used (or to be exact
it's 'bytes' instead of 'str' in Python 3). Unfortunately this does not
remove the need for the 'unicode' alias, but reduces it a bit.

Change-Id: I7118142b7881821d78e4cb848116c4a2e5721c0a
Merge "[IMPROV] Use str.decode instead of unicode"