only install orjson on cpython, pypy is ok with pure json

requirements.txt

@@ -12,10 +12,4 @@ ttfautohint-py==0.5.1
 
 # optional, for experimental reading/writing ufoLib2's UFO as json
 cattrs==23.1.2
-# orjson currently doesn't ship 32-bit wheels for Windows
-# https://github.com/ijl/orjson/issues/409
-# platform_machine environment marker returns 'AMD64' on Windows even if Python is 32-bit
-# so there's no way to tell pip to install orjson only on 64-bit Win Python; hence
-# don't install orjson on Windows (works fine without it using stdlib json module)
-# https://stackoverflow.com/a/75411662
-orjson==3.9.3
+orjson==3.9.3; platform_python_implementation == 'CPython'