Remove nexus.hc.to repository from pom.xml.

Jitpack is the recommended Vault repository now, and we've actually
already updated the comment for Jitpack to include Vault previously, so
let's just get rid of the HeroCraft repo now.

pom.xml

@@ -77,12 +77,6 @@
       <url>https://hub.spigotmc.org/nexus/content/groups/public/</url>
     </repository>
 
-    <!-- Vault repo -->
-    <repository>
-      <id>vault-repo</id>
-      <url>http://nexus.hc.to/content/repositories/pub_releases</url>
-    </repository>
-
     <!-- bStats repo -->
     <repository>
       <id>bstats-repo</id>