Clean out sharedlists (#14857)

lib/pure/collections/sharedlist.nim

@@ -94,10 +94,4 @@ proc deinitSharedList*[A](t: var SharedList[A]) =
   clear(t)
   deinitLock t.lock
 
-proc initSharedList*[A](): SharedList[A] {.deprecated: "use 'init' instead".} =
-  ## This is not posix compliant, may introduce undefined behavior.
-  initLock result.lock
-  result.head = nil
-  result.tail = nil
-
 {.pop.}