Align namespaces for unit tests

[mikkamp]

Changes proposed in this Pull Request:

There were several copy and paste errors for the namespaces being used in Unit tests. Because there were no conflicts this isn't a big deal, but this PR ensures the correct namespace is being used for each test. I also removed some unused import lines.

Detailed test instructions:

1. Install latest versions for unit testing bin/install-wp-tests.sh <db_name> <db_user> <db_pass>
2. Run unit tests vendor/bin/phpunit
3. Confirm that all tests continue to pass without issues

Changelog entry

• Dev - Align namespaces for unit tests.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 65.0%. Comparing base (ec86226) to head (30fa48f).
Report is 48 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff            @@
##             develop   #2561   +/-   ##
=========================================
  Coverage       65.0%   65.0%           
  Complexity      4588    4588           
=========================================
  Files            475     475           
  Lines          17900   17900           
=========================================
  Hits           11640   11640           
  Misses          6260    6260           

Flag	Coverage Δ
php-unit-tests	65.0% <ø> (ø)

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[martynmjones]

Hey @mikkamp, thanks for keeping our tests clean!

All tests are passing locally and the namespace changes and deletions all look good to me ✅