chore: remove unused commons-lang dependency from demo

it triggered a [security warning](https://github.com/apache/axis-axis2-java-core/security/dependabot/41)

Author: cortlepp

modules/samples/userguide/src/userguide/springbootdemo/pom.xml

@@ -152,11 +152,6 @@
             <artifactId>commons-codec</artifactId>
             <version>1.15</version>
         </dependency>
-        <dependency>
-            <groupId>commons-lang</groupId>
-            <artifactId>commons-lang</artifactId>
-            <version>2.6</version>
-        </dependency>
         <dependency>
             <groupId>commons-validator</groupId>
             <artifactId>commons-validator</artifactId>