Remove unsupported static declaration of inner classes

JDK 11 does not support static inner classes.

solr/modules/ltr/src/java/org/apache/solr/ltr/feature/Feature.java

@@ -302,7 +302,7 @@ public String toString() {
     }
 
     /** A 'recipe' for computing a feature */
-    public abstract static class FeatureScorer extends Scorer {
+    public abstract class FeatureScorer extends Scorer {
 
       protected final String name;
       private DocInfo docInfo;
@@ -342,7 +342,7 @@ public DocIdSetIterator iterator() {
      * A <code>FeatureScorer</code> that contains a <code>Scorer</code>, which it delegates to where
      * appropriate.
      */
-    public abstract static class FilterFeatureScorer extends FeatureScorer {
+    public abstract class FilterFeatureScorer extends FeatureScorer {
 
       protected final Scorer in;
 
@@ -380,7 +380,7 @@ public float getMaxScore(int upTo) throws IOException {
      * Default FeatureScorer class that returns the score passed in. Can be used as a simple
      * ValueFeature, or to return a default scorer in case an underlying feature's scorer is null.
      */
-    public static class ValueFeatureScorer extends FeatureScorer {
+    public class ValueFeatureScorer extends FeatureScorer {
       float constScore;
 
       public ValueFeatureScorer(FeatureWeight weight, float constScore, DocIdSetIterator itr) {

solr/modules/ltr/src/java/org/apache/solr/ltr/feature/OriginalScoreFeature.java

@@ -91,7 +91,7 @@ public FeatureScorer scorer(LeafReaderContext context) throws IOException {
       return new OriginalScoreScorer(this, originalScorer);
     }
 
-    public static class OriginalScoreScorer extends FilterFeatureScorer {
+    public class OriginalScoreScorer extends FilterFeatureScorer {
 
       public OriginalScoreScorer(FeatureWeight weight, Scorer originalScorer) {
         super(weight, originalScorer);

solr/modules/ltr/src/java/org/apache/solr/ltr/feature/SolrFeature.java

@@ -234,7 +234,7 @@ public FeatureScorer scorer(LeafReaderContext context) throws IOException {
     }
 
     /** Scorer for a SolrFeature */
-    public static class SolrFeatureScorer extends FilterFeatureScorer {
+    public class SolrFeatureScorer extends FilterFeatureScorer {
 
       public SolrFeatureScorer(FeatureWeight weight, Scorer solrScorer) {
         super(weight, solrScorer);

solr/test-framework/src/java/org/apache/solr/cloud/ZkTestServer.java

@@ -267,7 +267,7 @@ private void updateForFire(WatchedEvent event) {
       }
     }
 
-    private static class TestZKDatabase extends ZKDatabase {
+    private class TestZKDatabase extends ZKDatabase {
 
       private final WatchLimiter limiter;