Revert "Add cmake back as a pip dependency."

This reverts commit 8b9d0439.

Reverting this because the cmake pip pakage is still busted.  I've been
getting messages from many people about how it's breaking their
systems/installs.

setup.py

@@ -233,7 +233,7 @@ setup(
     zip_safe=False,
     # We need an older more-itertools version because v6 broke pytest (for everyone, not just dlib)
     tests_require=['pytest==3.8', 'more-itertools<6.0.0'],
-    install_requires=['cmake'],
+    #install_requires=['cmake'], # removed because the pip cmake package is busted, maybe someday it will be usable.
     packages=['dlib'],
     package_dir={'': 'tools/python'},
     keywords=['dlib', 'Computer Vision', 'Machine Learning'],