[trivial] [hotfix] Remove some code that somehow got copied

[Yurlungur]

PR Summary

In PR #1007 , I moved some of the string parameter template specializations into their own file. For whatever reason, this move didn't stick when the branch was merged, and the code is now duplicated. This PR removes the duplicated code, which prevents linking on some platforms.

PR Checklist

• Code passes cpplint
• New features are documented.
• Adds a test for any bugs fixed. Adds tests for new features.
• Code is formatted
• Changes are summarized in CHANGELOG.md
• Change is breaking (API, behavior, ...)
  • Change is additionally added to CHANGELOG.md in the breaking section
  • PR is marked as breaking
  • Short summary API changes at the top of the PR (plus optionally with an automated update/fix script)
• CI has been triggered on Darwin for performance regression tests.
• Docs build
• (@lanl.gov employees) Update copyright on changed files

[lroberts36]

LGTM

[AstroBarker]

Resolved phoebus compilation issue on Darwin. Thanks!