Remove the Hero Slider region TWIG template file from Vartheme BS5

Problem/Motivation

#3159252: Remove the region "Media Hero Slider" from Vartheme BS4
But the templates/regions/region--hero-slider.html.twig file was not removed on the time.

Proposed resolution

Remove the Hero Slider region TWIG template file

Remaining tasks

• ✅ File an issue about this project
• ✅ Remove the no longer needed TWIG file
• ✅ Testing to ensure no regression
• ➖ Automated unit/functional testing coverage
• ➖ Developer Documentation support on feature change/addition
• ➖ User Guide Documentation support on feature change/addition
• ➖ Update Release Notes and Update Helper on new feature change/addition
• ✅ Code review from 1 Varbase core team member
• ✅ Full testing and approval
• ✅ Credit contributors
• ✅ Review with the product owner
• ❌ Release varbase-9.1.0-beta1, vartheme_bs5-1.0.0-beta1

User interface changes

• N/A

API changes

• N/A

Data model changes

• N/A