GUACAMOLE-540: Remove unused imports.

guacamole-ext/src/main/java/org/apache/guacamole/net/auth/Credentials.java

@@ -20,8 +20,6 @@
 package org.apache.guacamole.net.auth;
 
 import java.io.Serializable;
-import java.util.regex.Matcher;
-import java.util.regex.Pattern;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpSession;