Drop the nose requirement

As we now use a new enough version of `numcodecs` to be free of the
`nose` requirement (not to mention `zarr` no longer directly uses
`nose`), drop `nose` from the requirements.

Author: jakirkham

requirements_dev.txt

@@ -15,7 +15,6 @@ idna==2.6
 mccabe==0.6.1
 monotonic==1.3
 msgpack-python==0.4.8
-nose==1.3.7
 numcodecs==0.5.3
 numpy==1.13.3
 packaging==16.8

windows_conda_dev.txt

@@ -4,7 +4,6 @@ fasteners
 flake8
 monotonic
 msgpack-python
-nose
 numcodecs
 numpy
 setuptools_scm