We previously used to remove our FOUC helper inside of the style injection to ensure content was shown as fast as possible.
This behavior, however, was problematic for a few reasons:
1. Large JavaScript chunks would take longer than an animation frame to parse, causing FOUC
1. Rendering would sometimes complete before an animation frame, causing improper effects
To fix the latter, we started removing the no FOUC helper **before** rendering, however, we never fixed the former by removing the dead code.
There's not a great way to test this because the FOUC is so fast and flaky, however, this code really shouldn't exist and isn't likely to be re-added (regress).
Also, we already have FOUC tests that occasionally flake, probably due to this.
Fixes#12448Fixes#13058Fixes#11195Fixes#10404
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