Remove Cython from requirements.txt (#2604)

Cython should be a dependency of the remaining packages in requirements.txt, so should be installed anyway even if not a direct requirement.

Remove Cython from requirements.txt (#2604)
fca16dc4 · Glenn Jocher · GitHub · 3bb41489 · fca16dc4
--- a/requirements.txt
+++ b/requirements.txt
 # pip install -r requirements.txt

 # base ----------------------------------------
-Cython
 matplotlib>=3.2.2
 numpy>=1.18.5
 opencv-python>=4.1.2