[BE] - remove Observation returns from simulator.py step and reset

[aclegg3]

Motivation and Context

Refactors the simulator.py API to:

• remove Observation return from step and reset. These are "environemt" API decisions. In general, stepping and resetting the world would not trigger any sensor collection or return.
• removes the automated and forced disabling of rendering/textures when Sensors are not pre-declared. Configuration should not be assuming what the user wants and forcing itself. Provides freedom to declare sensors after initialization.
• removes some deprecated and unused functions
• adds some additional docstrings to clarify the initialization, resetting, and wrapping done in python over the binding API

How Has This Been Tested

CI should pass for sim.
Will fail for habitat-lab until refactored in-line with new reset and step API expectations.

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.

[meta-cla]

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