[WIP] Remove outdated files in preparation for a 2.0.0 release.

[ctb]

• Is it mergeable?
• make test Did it pass the tests?
• make coverage Is the new code covered?
• Did it change the command-line interface? Only additions are allowed
  without a major version increment. Changing file formats also requires a
  major version number increment.
• Was a spellchecker run on the source code and documentation after
  changes were made?

[codecov]

Codecov Report

Merging #607 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #607   +/-   ##
=======================================
  Coverage   89.44%   89.44%           
=======================================
  Files          27       27           
  Lines        4227     4227           
  Branches       39       39           
=======================================
  Hits         3781     3781           
  Misses        446      446

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[ctb]

Added into #631, which updates docs and notebooks.