[Distributed] Remove outdated declaration of _executeDistributedTarget from DistributedActor.swift

The function should be (and is) declared in `DistributedActorSystem.swift`

Author: xedin

stdlib/public/Distributed/DistributedActor.swift

@@ -184,14 +184,3 @@ func __isLocalActor(_ actor: AnyObject) -> Bool {
 
 @_silgen_name("swift_distributedActor_remote_initialize")
 func _distributedActorRemoteInitialize(_ actorType: Builtin.RawPointer) -> Any
-
-// ==== Remote target accesss -------------------------------------------------
-
-@available(SwiftStdlib 5.6, *)
-@_silgen_name("swift_distributed_execute_target")
-func _executeDistributedTarget(
-    on: AnyObject,
-    _ targetName: UnsafePointer<UInt8>,
-    _ targetNameLength: UInt,
-    argumentBuffer: Builtin.RawPointer,
-    resultBuffer: Builtin.RawPointer) async throws