We typically drop an OS version support every fall (see iOS 14 task, iOS 15 task).

It's that time of year again to drop an OS version, since we will be adding one with iOS 26.

I am separating this out from T395169, which could delay this as we hash out the designs. T395169 will be about liquid glass and Xcode 26 support, and this task is only about dropping iOS 16 support.

• Remove availability checks that are no longer needed
• Fix any new warnings that pop up

Test Notes

TestFlight 7.9.2 (5975)

• Light regression with trait collection changes (dynamic type, set theme to default, and change your device to light/dark mode).
• Light regression testing of the wikitext source editor. We dropped TextKit 1 with this and are now exclusively on TextKit 2 (TextKit provides several text editing capabilities). Click on edit source on a long article, and perform formatting. No need to save the edits, just check if the formatting works as usual.