[Refactor]--Cleaup;Remove unused field/methods.

[jturner65]

Motivation and Context

In preparation for rewriting the asset load pipeline, I'm coming across some unused code in ResourceManager and the various mesh constructs, among other places. This PR is for removing these methods, so that the pending asset load functionality PRs will retain their focus :) . This PR also has a few minor refactors/cleanups that I've come across :

• Remove unused/unimplemented voxel function declaration from Simulator.h
• Make build script 'src_python' message a bit more relevant to the user
• Remove deprecated config field from default physics config

How Has This Been Tested

All local c++ and python tests pass

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have completed my CLA (see CONTRIBUTING)
• I have added tests to cover my changes.
• All new and existing tests passed.

[Skylion007]

@jturner65, feel free to use the codecov report to help find likely dead code.

[aclegg3]

Thanks for cleaning up. LGTM.