Remove re-definitions of _overrideLifetime()

- These have now propagated to become public in all the relevant sources of the stdlib.

Author: glessard

Sources/FoundationEssentials/Data/Data.swift

@@ -2970,53 +2970,3 @@ extension Data : Codable {
         }
     }
 }
-
-// TODO: remove once _overrideLifetime is public in the standard library
-/// Unsafely discard any lifetime dependency on the `dependent` argument. Return
-/// a value identical to `dependent` with a lifetime dependency on the caller's
-/// borrow scope of the `source` argument.
-@unsafe
-@_unsafeNonescapableResult
-@_alwaysEmitIntoClient
-@_transparent
-@lifetime(borrow source)
-internal func _overrideLifetime<
-  T: ~Copyable & ~Escapable, U: ~Copyable & ~Escapable
->(
-  _ dependent: consuming T, borrowing source: borrowing U
-) -> T {
-  dependent
-}
-
-/// Unsafely discard any lifetime dependency on the `dependent` argument. Return
-/// a value identical to `dependent` that inherits all lifetime dependencies from
-/// the `source` argument.
-@unsafe
-@_unsafeNonescapableResult
-@_alwaysEmitIntoClient
-@_transparent
-@lifetime(copy source)
-internal func _overrideLifetime<
-  T: ~Copyable & ~Escapable, U: ~Copyable & ~Escapable
->(
-  _ dependent: consuming T, copying source: borrowing U
-) -> T {
-  dependent
-}
-
-/// Unsafely discard any lifetime dependency on the `dependent` argument.
-/// Return a value identical to `dependent` with a lifetime dependency
-/// on the caller's exclusive borrow scope of the `source` argument.
-@unsafe
-@_unsafeNonescapableResult
-@_alwaysEmitIntoClient
-@_transparent
-@lifetime(&source)
-internal func _overrideLifetime<
-  T: ~Copyable & ~Escapable, U: ~Copyable & ~Escapable
->(
-  _ dependent: consuming T,
-  mutating source: inout U
-) -> T {
-  dependent
-}