Depend on the new txtq package

[wlandau]

Summary

bbqr is the custom file-based message queue I built for drake.

Related GitHub issues

• Ref: Try liteq #407, A quicker end to staged parallelism #369

Checklist

• I have read drake's code of conduct, and I agree to follow its rules.
• I have read the guidelines for contributing.
• I have listed any substantial changes in the development news.
• I have added testthat unit tests to tests/testthat to confirm that any new features or functionality work correctly.
• I have tested this pull request locally with devtools::check()
• This pull request is ready for review.
• I think this pull request is ready to merge.

[codecov-io]

Codecov Report

Merging #410 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #410   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          67     66    -1     
  Lines        5349   5261   -88     
=====================================
- Hits         5349   5261   -88

Impacted Files	Coverage Δ
R/mc_utils.R	100% <100%> (ø)	⬆️

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[wlandau]

Update bbqr is now txtq. @clarkfitzg wrote an even more bare-bones message queue that may eventually make its way into drake.