remove lockable-resources dependency

most people do not need the concurrency limits and whislt lockable resources is one way to acheive it, it does not need to be installed out of the box.

Removing from the aggregator, people that need it can choose to install it if they desire.

pom.xml

@@ -91,11 +91,6 @@
             <artifactId>workflow-scm-step</artifactId>
             <version>2.6</version>
         </dependency>
-        <dependency>
-            <groupId>org.6wind.jenkins</groupId>
-            <artifactId>lockable-resources</artifactId>
-            <version>2.3</version>
-        </dependency>
         <dependency>
             <groupId>${project.groupId}</groupId>
             <artifactId>workflow-cps</artifactId>