[test] use the stdlib _overrideLifetime functions

Author: glessard

test/SILOptimizer/Inputs/SpanExtras.swift

@@ -1,56 +1,5 @@
 import Builtin
 
-/// 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 {
-  // TODO: Remove @_unsafeNonescapableResult. Instead, the unsafe dependence
-  // should be expressed by a builtin that is hidden within the function body.
-  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 {
-  // TODO: Remove @_unsafeNonescapableResult. Instead, the unsafe dependence
-  // should be expressed by a builtin that is hidden within the function body.
-  dependent
-}
-
-@unsafe
-@_unsafeNonescapableResult
-@_alwaysEmitIntoClient
-@_transparent
-@lifetime(&source)
-internal func _overrideLifetime<
-  T: ~Copyable & ~Escapable, U: ~Copyable & ~Escapable
->(
-  _ dependent: consuming T, mutating source: inout U
-) -> T {
-  // TODO: Remove @_unsafeNonescapableResult. Instead, the unsafe dependence
-  // should be expressed by a builtin that is hidden within the function body.
-  dependent
-}
-
 // A MutableSpan<Element> represents a span of memory which
 // contains initialized `Element` instances.
 @frozen