Fix various warnings

Remove unused imports, unused fields and variables, unused private
methods and unnecessary @SuppressWarnings.

Change-Id: Iff3dbd9e2669fcaa7cb42c1accfddfb2ba82b6e0
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

gerrit-cache-h2/src/main/java/com/google/gerrit/server/cache/h2/H2CacheFactory.java

@@ -146,7 +146,7 @@ class H2CacheFactory implements PersistentCacheFactory, LifecycleListener {
     }
   }
 
-  @SuppressWarnings({"unchecked", "rawtypes", "cast"})
+  @SuppressWarnings({"unchecked", "cast"})
   @Override
   public <K, V> Cache<K, V> build(CacheBinding<K, V> def) {
     Preconditions.checkState(!started, "cache must be built before start");