Unshade the javax.mail and javax.activation jars

This change removes these jars from shading and changes the assemblies file so that they are included as is.

Original commit: elastic/x-pack-elasticsearch@695f5e2b20

pom.xml

@@ -319,8 +319,6 @@
                         <includes>
 			    <include>com.googlecode.owasp-java-html-sanitizer:owasp-java-html-sanitizer</include>
                             <include>com.google.guava:guava</include>
-                            <include>javax.mail:mail</include>
-                            <include>javax.activation:activation</include>
                         </includes>
                     </artifactSet>
                     <relocations>

src/main/assemblies/plugin.xml

@@ -21,5 +21,13 @@
                 <exclude>org.elasticsearch:elasticsearch</exclude>
             </excludes>
         </dependencySet>
+        <dependencySet>
+	  <outputDirectory>/</outputDirectory>
+          <useTransitiveDependencies>false</useTransitiveDependencies>
+          <includes>
+            <include>javax.mail:mail</include>
+            <include>javax.activation:activation</include>
+          </includes>
+        </dependencySet>
     </dependencySets>
 </assembly>