revert: Remove disk space regression hack fix

[matthewfeickert]

Description

The change on the VMs used for the Ubuntu builds that caused the disk space regression in PR #819 is getting rolled back (c.f. actions/virtual-environments Issue 709). As a result, the temporary hack fix of running apt-get clean before installation on the ubuntu-latest jobs is no longer necessary and can be reverted.

Checklist Before Requesting Reviewer

• Tests are passing
• "WIP" removed from the title of the pull request
• Selected an Assignee for the PR to be responsible for the log summary

Before Merging

For the PR Assignees:

• Summarize commit messages into a comprehensive review of the PR

* Revert apt-get clean hack fix for disk space regression (now resolved)
   - c.f. https://github.com/actions/virtual-environments/issues/709

[codecov]

Codecov Report

Merging #831 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #831   +/-   ##
=======================================
  Coverage   95.92%   95.92%           
=======================================
  Files          54       54           
  Lines        3016     3016           
  Branches      424      424           
=======================================
  Hits         2893     2893           
  Misses         78       78           
  Partials       45       45           

Flag	Coverage Δ
#unittests	95.92% <ø> (ø)

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