MNT: Remove deprecation as a dependency - I will roll my own decorator. Tweak

wxpython dependency

requirements-extra.txt

 indexed_gzip>=0.7.0,<1
-wxpython>=3.0.2.0,<4.1
+wxpython==4.*
 trimesh>=2.22.28,<3
 rtree==0.8.3

requirements.txt

 six==1.*
-deprecation>=1.*,<=2.*
 numpy==1.*
 scipy>=0.18
 nibabel>=2.2