Remove add issues modal code from issue boards [RUN ALL RSPEC] [RUN AS-IF-FOSS]

Merged Lukas 'Eipi' Eipert requested to merge remove-disabled-add-issues-modal into master

What does this MR do?

This feature has been disabled since 13.6 with a feature flag. Seems like we have not gotten any feedback that we should enable it, so let's remove it from the code base.

One motivation for removing it: It uses the Vue runtime template compiler. Removing this will bring us one step closer to shipping Vue without the template compiler which will bring a performance improvement across all pages.

Screenshots (strongly suggested)

N/A

Does this MR meet the acceptance criteria?

Conformity

Availability and Testing

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

  • Label as security and @ mention @gitlab-com/gl-security/appsec
  • The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
  • Security reports checked/validated by a reviewer from the AppSec team
Edited by Lukas 'Eipi' Eipert