cython is only a build requirement, not an install requirement

Author: tshirtman

setup.py

@@ -68,7 +68,6 @@ def getenv(key):
 # detect cython
 if PLATFORM != 'android':
     SETUP_REQUIRES.append('cython')
-    INSTALL_REQUIRES.append('cython')
 else:
     FILES = [fn[:-3] + 'c' for fn in FILES if fn.endswith('pyx')]