Remove an unused import

Author: junichi11

src/main/java/com/junichi11/netbeans/modules/github/issues/issue/ui/GitHubIssuePanel.java

@@ -100,7 +100,6 @@
 import org.eclipse.egit.github.core.PullRequestMarker;
 import org.eclipse.egit.github.core.RepositoryCommit;
 import org.eclipse.egit.github.core.User;
-import org.eclipse.egit.github.core.client.IGitHubConstants;
 import org.eclipse.egit.github.core.service.IssueService;
 import org.netbeans.api.annotations.common.CheckForNull;
 import org.openide.DialogDescriptor;