Remove unused import of CodeMirror in PreferencesBox

Change-Id: I5bde24b761ca4783704761f48fac23942d4be3d1

gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/PreferencesBox.java

diff --git a/gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/PreferencesBox.java b/gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/PreferencesBox.java
index f57e76e..5021758 100644
--- a/gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/PreferencesBox.java
+++ b/gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/PreferencesBox.java
@@ -54,7 +54,6 @@
 import com.google.gwt.user.client.ui.PopupPanel;
 import com.google.gwt.user.client.ui.ToggleButton;
 
-import net.codemirror.lib.CodeMirror;
 import net.codemirror.lib.ModeInjector;
 
 import java.util.HashMap;