Allow installation through setup.py install (but all docs specify to use pip) (#750)

Author: PGijsbers

setup.py

@@ -6,13 +6,6 @@
 with open("openml/__version__.py") as fh:
     version = fh.readlines()[-1].split()[-1].strip("\"'")
 
-# Using Python setup.py install will try to build numpy which is prone to failure and
-# very time consuming anyway.
-if len(sys.argv) > 1 and sys.argv[1] == 'install':
-    print('Please install this package with pip: `pip install -e .` '
-          'Installation requires pip>=10.0.')
-    sys.exit(1)
-
 if sys.version_info < (3, 5):
     raise ValueError(
         'Unsupported Python version {}.{}.{} found. OpenML requires Python 3.5 or higher.'