Removal of ngx-text-diff package

[pjmonks]

The Renovate pull requests have found an artefact issue with package-lock.json:

npm ERR! code EINVALIDTAGNAME
npm ERR! Invalid tag name "^>=6.0.0" of package "@angular/cdk@^>=6.0.0": Tags may not have any characters that encodeURIComponent encodes.

npm ERR! A complete log of this run can be found in:
npm ERR!     /tmp/renovate-cache/others/npm/_logs/2022-05-27T12_36_03_963Z-debug-0.log

This issue comes from the package ngx-text-diff because it has set its peer dependencies using a legacy syntax. This issue explains more: ABenassi87/ngx-text-diff#62

However, this package isn't actually used, so the simplest way to resolve this is to remove it from the package.json list completely.