Remove trailing code from previous version

Author: odersky

compiler/src/dotty/tools/dotc/core/Contexts.scala

@@ -522,7 +522,6 @@ object Contexts {
     def outer: Context = _outer
 
     private var _period: Period = uninitialized
-      _period = period
     final def period: Period = _period
 
     private var _mode: Mode = uninitialized