[ENG-3748] Simplify branded reg pages to just use brand background img

[futa-ikeda]

• Ticket: ENG-3748
• Feature flag: n/a

Purpose

• Remove some of the complexities around how we use brand colors and images in the registries header

Summary of Changes

• Remove the logic pertaining to how we show brand color/images on the registries header, so the only thing shown in the header will just be the brand's hero image
• Accessibility/color contrast on branded registry pages is gonna be a little whacky until we change the brand assets to a more appropriate color

Screenshot(s)

• A lot of the external registries will look funny until their brand assets are updated, so I imagine most registries won't look good until those images are updated

• Before (Solid brand primary color background with 40% opacity and greyscaled image on top) :
  

• After (Just the image, no greyscale or opacity) :
  

Side Effects

• Community-operated registries will need to go over their branding and update the logos/banner images accordingly

QA Notes

• We have a number of community operated registries and their assets will need to be updated to have sufficient color contrast

[brianjgeiger]

🎉

[coveralls]

Pull Request Test Coverage Report for Build 3023252619

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 71.302%

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Totals
Change from base Build 3023240060:	0.0%
Covered Lines:	5385
Relevant Lines:	7338

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💛 - Coveralls