CI: check for numpy.random-related imports
~~- [x] closes #37053 (keep this issue open until both #37492 and #37117 are completed)~~
- [x] tests added / passed ~~(once #37492is merged)~~

# update 2020-10-31
now use a pre-commit check instead of the previous code_check

*** 
~~code_check.sh will be used to locate where numpy.random-related imports are.~~ See the separate script to do the whole clean-up in https://github.com/pandas-dev/pandas/pull/37103#issue-502582592.