FE-1039 FE-1048 Fixes on images

[PavlosTze]

Includes

• Fix static images directories
• Fix images naming, use only lowercase with hyphens
• Remove not used images
• Fixed the size of images in "Rewards Claiming" and "How to join Arbitrum" pages

How to test?

Branch Preview URL: https://feature-icon-names-fixes.docs-33x.pages.dev

1. Navigate throughout our docs and make sure all images are visible.
2. Ensure that the images in the "Rewards Claiming" and "How to join Arbitrum" look OK

Other?

Removed "Video Instructions" section from D1, Helium and Pulse as these refer to M5 and feel out of context there.

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