Remove unnecessary _fixLifetime

Author: Catfish-Man

stdlib/public/core/StringCreate.swift

@@ -124,7 +124,6 @@ extension String {
       // we use it directly. This could be a little faster, but this error path
       // shouldn't be perf-sensitive anyway.
       let temporaryCodeUnits = Array(result.codeUnits)
-      defer { _fixLifetime(temporaryCodeUnits) }
       return temporaryCodeUnits.withContiguousStorageIfAvailable {
         //This could be optimized to use excess tail capacity
         return repairUTF8($0, firstKnownBrokenRange: initialRange)