Use installer outputs & Fix (de)activate scripts

[leofang]

Close #2.

This PR does 3 things:

1. Use Windows installer and install (not extract!) to $PREFIX\Library
2. Fix (de)activate scripts to not print debug messages in user environments
3. Erase the pre-installed MPI from Conda-Forge's VM image so that downstream packages can test MPI against msmpi

Checklist

• [x] Used a personal fork of the feedstock to propose changes
• [x] Bumped the build number (if the version is unchanged)
• [ ] Reset the build number to 0 (if the version changed)
• [x] Re-rendered with the latest conda-smithy (Use the phrase code>@<space/conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• [x] Ensured the license file is being packaged.

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[leofang]

@conda-forge-admin, please rerender

[github-actions[bot]]

Hi! This is the friendly automated conda-forge-webservice. I tried to rerender for you, but it looks like there was nothing to do.

[leofang]

Hmmm, ok, so if we remove the old MPI runtime and then install, -installroot will work...Interesting.

[leofang]

Hmmm, ok, so if we remove the old MPI runtime and then install, -installroot will work...Interesting.

I should have noticed this in https://github.com/conda-forge/msmpi-feedstock/pull/7/commits/ddccb520f0683468179129660a51ea8f3b091d55 from #7!!!

https://dev.azure.com/conda-forge/feedstock-builds/_build/results?buildId=308809&view=results

[leofang]

PR description updated. Note that using the installer properly should fix the 32 vs 64 bit issue (default is 32 bit if extracting from the exe directly)...

[leofang]

Verified working in downstream packages:

• https://github.com/conda-forge/mpi4py-feedstock/pull/43
• pybind11-mpi4py (https://github.com/mpi4py/mpi4py/issues/19#issuecomment-829398857)