--[BE Week]Remove shadowmanager/variance shadow map code

[jturner65]

Motivation and Context

This PR removes the variance shadow map-based shadow functionality demo code. It was not being used, required expansion, and we have decided to pursue other routes for shadow-like graphical performance, planning on integrating HBAO into the simulator in the next few months.

How Has This Been Tested

Current 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.

[0mdc]

Here are some remaining references:

pbrUniforms.glsl L31
gaussianFilter.frag L32
esp/gfx/PbrShader.h L640

[0mdc]

LGTM!