Remove testing module.

[vyasr]

Description

Remove the testing module.

Motivation and Context

See glotzerlab/signac#709

Checklist:

• I am familiar with the Contributing Guidelines.
• I agree with the terms of the Contributor Agreement.
• My name is on the list of contributors.
• The changes introduced by this pull request are covered by existing or newly introduced tests.
• The package documentation and framework documentation in signac-docs are up to date with these changes.
• I have updated the changelog and added any related issue and pull request numbers for future reference.

[codecov]

Codecov Report

Merging #691 (373a989) into master (3a2177a) will increase coverage by 0.07%.
The diff coverage is n/a.

❗ Current head 373a989 differs from pull request most recent head ca75b39. Consider uploading reports for the commit ca75b39 to get more accurate results

@@            Coverage Diff             @@
##           master     #691      +/-   ##
==========================================
+ Coverage   80.21%   80.29%   +0.07%     
==========================================
  Files          31       30       -1     
  Lines        3144     3136       -8     
  Branches      675      675              
==========================================
- Hits         2522     2518       -4     
+ Misses        489      485       -4     
  Partials      133      133              

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[bdice]

One small fix to the changelog, otherwise LGTM.