Remove local definitions of `_overrideLifetime()`

[glessard]

By a stroke of bad timing, the attempted removal of these functions in #1400 was premature, as a compiler the Foundation framework is required to support did not receive swiftlang/swift#81224 on the expected schedule. We will remove these (reverting #1438) once we are in a less critical period for integration.

Also tracked as rdar://155973325.

[glessard]

We were able to wait until the landed everywhere necessary, making this change unneeded.