refactor: switch to new location of itemInputHelpText, in help.ts

[rossiam]

I know I said two pull request for adding sub-command and topic help in the last one but I've decided to add a third since this naturally breaks out. (I might just do the rest of it in multiple PRs too since there will be a lot of files touched.)

This pull request removes the old copy of itemInputHelpText and updates references to it to use the new location.

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Latest commit: cac8c4e

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