Remove deprecated_addNit.

pkg/front_end/messages.yaml

 # Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # Each entry in this map corresponds to a diagnostic message. Ideally, each
 # entry contains three parts:
 #
 # 1. A message template (template).
 #
 # 2. A suggestion for how to correct the problem (tip).
@@ skipping 603 matching lines @@
   template: "Couldn't find previous token."
 
 InternalProblemStackNotEmpty:
   template: "#name.stack isn't empty:\n  #string"
 
 InternalProblemAlreadyInitialized:
   template: "Attempt to set initializer on field without initializer."
 
 InternalProblemBodyOnAbstractMethod:
   template: "Attempting to set body on abstract method."
+
+LocalDefinitionHidesExport:
+  template: "Local definition of '#name' hides export from '#uri'."
+
+LocalDefinitionHidesImport:
+  template: "Local definition of '#name' hides import from '#uri'."
+
+ExportHidesExport:
+  template: "Export of '#name' (from '#uri') hides export from '#uri2'."
+
+ImportHidesImport:

[sra1, 2017/07/11 19:27:44]

Why do we warn about this?
It is only a problem if the import is used, and that is an error.

[ahe, 2017/07/12 15:48:17]

A warning is required when the import is used, a warning is emitted using this
message.

However, I also generate a "nit" which was supposed to be silent but helpful for
debugging (in --verbose) mode.

+  template: "Import of '#name' (from '#uri') hides import from '#uri2'."
+
+DuplicatedExport:
+  template: "'#name' is exported from both '#uri' and '#uri2'."
+
+DuplicatedImport:
+  template: "'#name' is imported from both '#uri' and '#uri2'."