Preprints branding update (#1922)

-   Ticket: []
-   Feature flag: n/a

## Purpose
- Remove possible failure point by not using preprintProvider.asset
- Add special casing to address nutrixiv's navbar color https://osf.io/preprints/nutrixiv/

## Summary of Changes
- Remove use of ThemeStyles from preprint (this set the navbar logo to use the preprintProvider.asset. square_color_transparent, when we want to just use the brand. topnavLogoImage going forward)
- Add special case for nutrixiv to use a white background similar to biohackrxiv

app/preprints/template.hbs

@@ -1,6 +1,5 @@
 {{page-title this.theme.provider.providerTitle replace=true}}
 <div {{with-branding (get-model this.theme.provider.brand)}}>
-    <ThemeStyles />
     <BrandedNavbar
         @translateKey='collections.general.brand'
         @brandRoute='preprints.discover'