Remove Win32 byte-order swapping in UniFromEnc

Reference: 513d4f79ed811dc44b8611aabfa9113276fd44a9
It seems that iconv has been updated since then, or something has changed so
that the correct value is returned without byte-order swapping.
Merge pull request #1442 from jtanx/encoding

Remove Win32 byte-order swapping in UniFromEnc