Docs: redefinition of stdlib functions causing invalid cross references. #6737

Reporting a bug

• I have tried using the latest released version of Numba (most recent is
  visible in the change log (https://github.com/numba/numba/blob/master/CHANGE_LOG).
• N/A I have included a self contained code sample to reproduce the problem.
  i.e. it's possible to run as 'python bug.py'.

Following on from #6619 (comment) the doc pages that come from "autogeneration" via numba.misc.help.inspector redefine functions from python stdlib modules, e.g. math.sin, as a result referring to :func:`math.sin` in docs leads to a link being generated to the Numba redefinition opposed to the Python docs.