Remove sphinx_thebe conf and dependency

[rohanbabbar04]

Closes #463

Description

• As suggested in Improve Docs for predictive functions #468
• Remove thebe from conf.py
• Remove thebe from requirements.

Checklist

• Code style is correct (follows pylint and black guidelines)
• Includes new or updated tests to cover the new feature
• New features are properly documented (with an example if appropriate)
• Includes a sample plot to visually illustrate the changes (only for plot-related functions)
• Widget states have been properly saved (only for notebooks with widgets) see for details.