Remove deprecated_internalProblem.

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 565 matching lines @@
   template: "Internal error: Unhandled #string in #string2."
 
 Unimplemented:
   template: "Internal error: Unimplemented #string."
 
 Unexpected:
   template: "Internal error: Expected '#string', but got '#string2'."
 
 Unsupported:
   template: "Internal error: Unsupported operation: '#name'."
+
+InternalProblemSuperclassNotFound:
+  template: "Internal error: Superclass not found '#name'."
+
+InternalProblemNotFound:
+  template: "Internal error: Couldn't find '#name'."
+
+InternalProblemNotFoundIn:
+  template: "Internal error: Couldn't find '#name' in '#name2'."
+
+InternalProblemPrivateConstructorAccess:
+  template: "Internal error: Can't access private constructor '#name'."
+
+InternalProblemConstructorNotFound:
+  template: "Internal error: No constructor named '#name' in '#uri'."
+
+InternalProblemExtendingUnmodifiableScope:
+  template: "Can't extend an unmodifiable scope."
+
+InternalProblemPreviousTokenNotFound:
+  template: "Couldn't find previous token."
+
+InternalProblemStackNotEmpty:
+  template: "Internal error: #name.stack isn't empty:\n  #string"
+
+InternalProblemAlreadyInitialized:
+  template: "Internal error: Attempt to set initializer on field without initializer."
+
+InternalProblemBodyOnAbstractMethod:
+  template: "Internal error: Attempting to set body on abstract method."