refactor library prefix suggestion generation

pkg/analysis_server/test/services/completion/local_computer_test.dart

 // Copyright (c) 2014, 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.
 
 library test.services.completion.dart.local;
 
 import 'package:analysis_server/src/services/completion/local_computer.dart';
 import 'package:unittest/unittest.dart';
 
 import '../../reflective_tests.dart';
@@ skipping 64 matching lines @@
     ' class _B {}' //
     ' A T;');
     expect(computeFast(), isTrue);
     var a = assertSuggestClass('A');
     expect(a.element.isDeprecated, isTrue);
     expect(a.element.isPrivate, isFalse);
     var b = assertSuggestClass('_B');
     expect(b.element.isDeprecated, isFalse);
     expect(b.element.isPrivate, isTrue);
     assertSuggestTopLevelVar('T', 'A');
-    assertSuggestLibraryPrefix('x');
+    // Library prefix suggestion is provided by ImportedComputer
+    assertNotSuggested('x');
   }
 
   test_ExpressionStatement_name() {
     // ExpressionStatement  Block
     addTestSource('class A {a() {var f; A ^}}');
     expect(computeFast(), isTrue);
     assertNotSuggested('A');
     assertNotSuggested('a');
     assertNotSuggested('f');
   }
@@ skipping 131 matching lines @@
 
         // VariableDeclaration  VariableDeclarationList  VariableDeclarationStatement
     addTestSource('class A {a() {var f; {var x;} var e = ^ var g;}}');
     expect(computeFast(), isTrue);
     assertSuggestClass('A');
     assertSuggestLocalVariable('f', null);
     assertNotSuggested('g');
     assertNotSuggested('x');
   }
 }