Remove unidecode (for anyascii), pandoc, poppler, and tbb

[Zeitsperre]

Overview

This PR addresses issues raised in #494

Changes:

• Replaced unidecode (GPLv2) with anyascii (MIT)
• Removed pandoc, poppler, and tbb from conda environment dependencies

Related Issue / Discussion

There are still some final issues with the licensing for cartopy which changed from LGPL to BSD-3-Clause in version 0.23. This update will force us to drop Python3.8. I'll address this in a new Pull Request.

[tlvu]

LGTM. Are pandoc, poppler, and tbb being dropped also due to licensing issues or they are unused? The reason is not apparently clear to me.

[tlvu]

I am guessing a matching dependencies cleanup PR will also be needed on conda packaging side?

[Zeitsperre]

Are pandoc, poppler, and tbb being dropped also due to licensing issues or they are unused? The reason is not apparently clear to me.

As far as I can tell, these dependencies are not needed to run the library (in addition to being under GPL/copyleft licenses):

• pandoc is needed to convert documentation to other formats (this can be done already in ReadTheDocs/sphinx directly)
• tbb and poppler are never called in the code

The changes will eventually be ported to the conda-forge package as well!