[12.x] Remove images that have been replaced in core

Problem/Motivation

This ticket is to house images that should be removed in D12

Steps to reproduce

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Proposed resolution

In 📌 Update loading icon and use SVG Needs review
> core/misc/loading-small.gif
> core/misc/loading.gif
> core/themes/starterkit_theme/images/icons/loading-small.gif

In #1974928: Update Drupal's default throbber icons →
> core/misc/throbber-active.gif
> core/misc/throbber-inactive.png

Remaining tasks

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User interface changes

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API changes

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Data model changes

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Release notes snippet

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