[stdlib] remove a repetition

Author: glessard

stdlib/public/core/StringUTF8View.swift

@@ -337,13 +337,7 @@ extension String.UTF8View {
 #if _runtime(_ObjC)
       // handle non-UTF8 Objective-C bridging cases here
       if !_guts.isFastUTF8 && _guts._object.hasObjCBridgeableObject {
-        let storage: __StringStorage
-        if let associated = _guts.getAssociatedStorage() {
-          storage = associated
-        }
-        else {
-          storage = _guts.getOrAllocateAssociatedStorage()
-        }
+        let storage = _guts.getOrAllocateAssociatedStorage()
         let (start, count) = unsafe (storage.start, storage.count)
         let span = unsafe Span(_unsafeStart: start, count: count)
         return unsafe _overrideLifetime(span, borrowing: self)