DLSV2-648 Replaces and removes html tag removal string in signposting helper

[manishagarwalnhs]

JIRA link

DLSV2-648

Description

The new helper handles null and empty strings. We have replaced references to the old method SignpostingHelper.DisplayText() with the new method DisplayStringHelper.RemoveMarkup and removed the old method from the solution.

Screenshots

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Developer checks

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I have:

• Run the formatter and made sure there are no IDE errors.
• Written tests for the changes (accessibility tests, unit tests for controller, data services, services, view models, etc)
• Manually tested my work with and without JavaScript. Full manual testing guidelines can be found here: https://softwiretech.atlassian.net/wiki/spaces/HEE/pages/6703648740/Testing
• Updated/added documentation in Swiki and/or Readme. Links (if any) are below:
  • doc_1_here
• Updated my Jira ticket with information about other parts of the system that were touched as part of the MR and have to be sanity tested to ensure nothing’s broken.
• Scanned over my own MR to ensure everything is as expected.