Revert "Add regression test for rdar://148357926"

This reverts commit 373d08e.

Author: hamishknight

test/Constraints/opened_existentials.swift

@@ -565,29 +565,3 @@ do {
     types.assertTypesAreEqual()
   }
 }
-
-struct G<A>: PP3 {}
-
-protocol PP1 {
-    associatedtype A
-}
-
-extension PP1 {
-    func f(p: any PP2<G<Self.A>>) {
-        p.g(t: self)
-    }
-}
-
-protocol PP2<B> {
-    associatedtype A
-    associatedtype B: PP3 where Self.B.A == Self.A
-}
-
-extension PP2 {
-    func g<T: PP1>(t: T) where Self.B == G<T.A> {}
-}
-
-protocol PP3 {
-    associatedtype A
-}
-