Remove unused compat shim for 'bytes'

[jdufresne]

Never used. Both Python 2.7 and Python 3 have the type bytes. On Python
2.7 it is an alias for str, same as what was previously defined.

[Julian]

Not a click author, but seems to me that it's unlikely that the point of that line was to be "useful", otherwise the next line (raw_input = raw_input) is even more transparently pointless.

I suspect instead that the point is to explicitly list each cross-compatible name that is to be made available.

[jdufresne]

The next line raw_input = raw_input is required as Python 2 & 3 have differences in input handling. See:

https://docs.python.org/3/whatsnew/3.0.html#builtins

PEP 3111: raw_input() was renamed to input(). That is, the new input() function reads a line from sys.stdin and returns it with the trailing newline stripped. It raises EOFError if the input is terminated

The raw_input needs to be always be importable from _compat.py to make this transparent to uses in click.

This is not true of bytes. Both Python 2 & 3 have the type bytes. So there is no need to define it explicitly as a compatability shim. Observe:

$ python2
>>> bytes
<type 'str'>

bytes is never imported from _compat.py.

Therefore, I still believe this is a cleanup of unused code.