Remove matplotlib from conda requirements.

[0mdc]

Motivation and Context

This changeset removes the matplotlib dependency from the conda build requirements.
This dependency includes many others that are likely to conflict with an environment.

How Has This Been Tested

N/A

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.

[aclegg3]

For context, the only imports of matplotlib in our code are for displaying sensor images in plots for the tutotials like here:

habitat-sim/examples/tutorials/nb_python/ECCV_2020_Advanced_Features.py

Line 679 in f3089bc

plt.figure(figsize=(12, 8))

These can probably just be replaced by Pillow image show commands and related utils to remove matplotlib entirely.

This refactor can be a follow-up to removing the requirement.