Adding remove_row_type()

[ddsjoberg]

What changes are proposed in this pull request?
Added function remove_row_type().

If there is an GitHub issue associated with this pull request, please provide link.
closes #678

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Checklist for PR reviewer

• PR branch has pulled the most recent updates from master branch. Ensure the pull request branch and your local version match and both have the latest updates from the master branch.
• If an update was made to tbl_summary(), was the same change implemented for tbl_svysummary()?
• If a new function was added, function included in _pkgdown.yml
• If a bug was fixed, a unit test was added for the bug check
• Run pkgdown::build_site(). Check the R console for errors, and review the rendered website.
• Code coverage is suitable for any new functions/features. Review coverage with covr::report(). Before you run, set Sys.setenv(NOT_CRAN=true) and begin in a fresh R session without any packages loaded.
• R CMD Check runs without errors, warnings, and notes
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• When the branch is ready to be merged into master, increment the version number using usethis::use_version(which = "dev"), run codemetar::write_codemeta(), approve, and merge the PR. Please use "Suash and merge".