Properly fix JavaDoc linting issues

Fixes our own, and upstream's, issues with the stricter Java 8 JavaDoc
linter.

Also removes the destroystokyo-release maven repository. I'm not sure
why I added it originally, but it's unnecessary now.

pom.xml

@@ -40,10 +40,6 @@
             <id>aikar</id>
             <url>http://ci.emc.gs/nexus/content/groups/aikar/</url>
         </repository>
-        <repository>
-            <id>destroystokyo-releases</id>
-            <url>https://repo.destroystokyo.com/repository/maven-releases/</url>
-        </repository>
     </repositories>
 
     <distributionManagement>