remove reading longdesc from missing files in setup.py

[mzizzi]

Attempting to pip install the latest release produces the following error:

$ pip install python-libxdo==0.1.2a0
Collecting python-libxdo==0.1.2a0
  Using cached python-libxdo-0.1.2a0.tar.gz
    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/pip-build-rdQkct/python-libxdo/setup.py", line 13, in <module>
        with open(os.path.join(here, 'CHANGELOG.rst')) as fp:
    IOError: [Errno 2] No such file or directory: '/tmp/pip-build-rdQkct/python-libxdo/CHANGELOG.rst'

I assume this is because sdist doesn't bundle the changelog or readme in the source tarball unless they are explicitly listed in a manifest file.

This PR removes the reading those file into longdesc which was not being used.