Set zip_safe = False to disable egg installation (#842)

Currently `setuptools` assumes that torhcaudio is zip safe and performs
egg (zip) installation when `python setup.py install` (or `pip install .`).

When `torchaudio` loads extension module written with Torchscript, 
the corresponding loading function requires the `so` file to be present as 
an actual file, and this does not work well with egg installation.

This CC fixes this by setting `zip_safe=False` in setup.py and disable egg
installation, so that `python setup.py install` installs uncompressed files
with regular directory structure.

setup.py

@@ -85,5 +85,6 @@ setup(
     cmdclass={
         'build_ext': setup_helpers.BuildExtension.with_options(no_python_abi_suffix=True)
     },
-    install_requires=[pytorch_package_dep]
+    install_requires=[pytorch_package_dep],
+    zip_safe=False,
 )