smtp-tasks: remove redundant dependency

maven-shade-plugin complained about overlapping classes between javax.activation-1.2.0.jar and activation-1.1.jar.

Author: ibodrov

plugins/tasks/smtp/pom.xml

@@ -36,6 +36,12 @@
         <dependency>
             <groupId>com.sun.mail</groupId>
             <artifactId>javax.mail</artifactId>
+            <exclusions>
+                <exclusion>
+                    <groupId>javax.activation</groupId>
+                    <artifactId>activation</artifactId>
+                </exclusion>
+            </exclusions>
         </dependency>
         <dependency>
             <groupId>com.sun.activation</groupId>