only trigger livereload by .css files

[torhoehn]

Description (*)

• Reverted Enable livereload for watch:<theme> commands #10836
• Confirmed by Grunt watch triggers entire page reload #19544 (comment)_

Fixed Issues (if relevant)

1. Grunt watch triggers entire page reload #19544: Grunt watch triggers entire page reload

Manual testing scenarios (*)

1. Run grunt watch and change a .less file
2. less changes triggers styles refresh without reloading entire page

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[m2-assistant]

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[magento-engcom-team]

Hi @rogyar, thank you for the review.
ENGCOM-4733 has been created to process this Pull Request

[VasylShvorak]

✔️ QA passed

[magento-engcom-team]

Hi @VladimirZaets, thank you for the review.
ENGCOM-4733 has been created to process this Pull Request

[m2-assistant]

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