FXDE in-product pages include navbar

[janbrasna]

When compared to release/beta:
https://www-dev.allizom.org/en-CA/firefox/127.0/whatsnew/
https://www-dev.allizom.org/en-CA/firefox/126.0beta/whatsnew/
and nightly:
https://www-dev.allizom.org/en-US/firefox/80.0a1/whatsnew/

the WNPs and firstrun for aurora/developer currently start with the common layout masthead:
https://www-dev.allizom.org/en-US/firefox/102.0a2/whatsnew/
https://www-dev.allizom.org/en-US/firefox/92.0a2/whatsnew/
https://www-dev.allizom.org/en-US/firefox/83.0a2/firstrun/

(comparison aurora–beta:)

(whatsnew aurora × nightly:)

(firstrun aurora × nightly:)

Is it intentional, or for consistency with other in-product pages this should also skip the masthead?

[janbrasna]

Why I'm raising this is that in #14936 this is being evened out for all channels in simplification, so the FXDE WNPs would also be header-less — therefore I've added the same treatment to its firstrun for consistency:

(current × removed:)

(Unless the navbar there is intentional, and I'll have to find a way to make the aurora in-product pages behave differently.)