Clean up unused variable.

Fixes an analyzer warning when building externally with Dart SDK 2.0.0-dev.4.0.

PiperOrigin-RevId: 173269173

Author: nshahan

lib/model/ui/highlighted_text_model.dart

@@ -4,7 +4,6 @@
 
 import 'dart:math' show max;
 
-import 'package:logging/logging.dart';
 import 'package:meta/meta.dart';
 import 'package:quiver/core.dart' show hash2;
 
@@ -33,9 +32,6 @@ class HighlightedTextSegment {
   String toString() => isHighlighted ? "*$text*" : text;
 }
 
-final Logger _logger =
-    new Logger('angular_components.module.ui.highlighted_text_model');
-
 /// A class to highlight the occurrences of a list of tokens within a string.
 /// By default, matches are only highlighted at the start of words,
 /// and matching is case-insensitive.