Stop displaying 'added from url placeholder'

[cbeer]

Fixes #3270

I've left the i18n strings in place, on the off-chance they are used downstream or in plugins 🤷

[codecov-commenter]

Codecov Report

Merging #3448 (9d7fe2d) into master (453f1a3) will not change coverage.
The diff coverage is n/a.

❗ Current head 9d7fe2d differs from pull request most recent head 2de7f22. Consider uploading reports for the commit 2de7f22 to get more accurate results

@@           Coverage Diff           @@
##           master    #3448   +/-   ##
=======================================
  Coverage   88.91%   88.91%           
=======================================
  Files         198      198           
  Lines        3409     3409           
=======================================
  Hits         3031     3031           
  Misses        378      378           

Impacted Files	Coverage Δ
src/components/ManifestListItem.js	92.85% <ø> (ø)

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