Fix utils.py for PyPy on Windows

The line
```python
from __future__ import unicode_literals
```
introduced in commit [ecc0c5ee01f0e5bdd6af0c32cb5b4adcb2a2f78c](https://github.com/rg3/youtube-dl/commit/ecc0c5ee01f0e5bdd6af0c32cb5b4adcb2a2f78c) broke youtube-dl for PyPy on Windows, making it unable to locate WinAPI functions.
Error: "TypeError: function name must be a string or integer"

Adding "b" prefix to strings with WinAPI function names fixes it.
Revert "[utils] Work around PyPy stupidity with Windows DLLs (Fixes #4392)"

This reverts commit 16040f46d64bad8dcc5f948288ef469dd787d3d3.
Merge remote-tracking branch 'grompe/patch-1'