Remove packages and package_dir from setup.py

I really am not sure why, but this has been causing big headaches for
use with scikit build. Probably some hard-to-track bug.

Basically, if we kept these lines the way that they are, all of the
targets `install()`ed by cmake get installed in a completely different
location than the rest of the packages. They get installed in "stempy"
in the root directory of the environment instead of inside
lib/pythonX.X/site-packages/stempy. I really don't know why, but since
we can seemingly do things fine without those lines, just remove them.

Signed-off-by: Patrick Avery <patrick.avery@kitware.com>

setup.py

@@ -27,8 +27,7 @@ def extra_cmake_args():
         'Programming Language :: Python :: 3',
     ],
     keywords='',
-    packages=['stempy', 'stempy.io', 'stempy.image', 'stempy.pipeline'],
-    package_dir={'':'python'},
+    packages=['stempy'],
     install_requires=[
         'numpy',
         'h5py',