deprecate `T` `Ts` `P` and `Fn` in python 3.12+

[DetachHead]

they aren't needed due to new generic syntax

[KotlinIsland]

So we gonna deprecated them in 7 years?

[DetachHead]

once we have a way to deprecate things that aren't functions or classes, we should deprecate them in an if sys.version_info >= (3, 12): ... block

[KotlinIsland]

why doesn't deprecated have a condition/when flag?

@deprecated("asdf", when=sys.version_info >= (3, 12))
def f(): ...