Fix miscellaneous compiler warnings

Remove unused imports, remove unused local variables, parameterize
generic types, suppress warnings.

Change-Id: I8e4867d9a03ff774c1f8e04ff9853b0afb676e69
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

gerrit-server/src/main/java/com/google/gerrit/rules/PrologEnvironment.java

@@ -82,6 +82,7 @@ public class PrologEnvironment extends BufferingPrologControl {
    * @param sv unique key.
    * @return the value; null if not stored.
    */
+  @SuppressWarnings("unchecked")
   public <T> T get(StoredValue<T> sv) {
     return (T) storedValues.get(sv);
   }
@@ -93,6 +94,7 @@ public class PrologEnvironment extends BufferingPrologControl {
    * @param sv unique key.
    * @param obj the value to store under {@code sv}.
    */
+  @SuppressWarnings("unchecked")
   public <T> void set(StoredValue<T> sv, T obj) {
     storedValues.put((StoredValue<Object>) sv, obj);
   }