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.

Spigot-API-Patches/PlayerTeleportEndGatewayEvent.patch

@@ -7,7 +7,7 @@ Allows you to access the Gateway being used in a teleport event
 
 diff --git a/src/main/java/com/destroystokyo/paper/event/player/PlayerTeleportEndGatewayEvent.java b/src/main/java/com/destroystokyo/paper/event/player/PlayerTeleportEndGatewayEvent.java
 new file mode 100644
-index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000
+index 00000000..bdefbc9f
 --- /dev/null
 +++ b/src/main/java/com/destroystokyo/paper/event/player/PlayerTeleportEndGatewayEvent.java
 @@ -0,0 +0,0 @@
@@ -31,7 +31,8 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +
 +    /**
 +     * The gateway triggering the teleport
-+     * @return
++     *
++     * @return EndGateway used
 +     */
 +    public EndGateway getGateway() {
 +        return gateway;