Correct quantized HNSW validation to be in-line with HNSW (#13263)

When intra-merge parallelism was introduced, the validation that numWorkers must ==1 with a null executor service was removed from Lucene99HnswVectorsFormat. However, I forgot to remove that validation from Lucene99HnswScalarQuantizedVectorsFormat.

This corrects that mistake, allowing Lucene99HnswScalarQuantizedVectorsFormat and Lucene99HnswVectorsFormat to take advantage of the merge-schedulers intra-merge threading.

lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99HnswScalarQuantizedVectorsFormat.java

@@ -120,10 +120,6 @@ public Lucene99HnswScalarQuantizedVectorsFormat(
     }
     this.maxConn = maxConn;
     this.beamWidth = beamWidth;
-    if (numMergeWorkers > 1 && mergeExec == null) {
-      throw new IllegalArgumentException(
-          "No executor service passed in when " + numMergeWorkers + " merge workers are requested");
-    }
     if (numMergeWorkers == 1 && mergeExec != null) {
       throw new IllegalArgumentException(
           "No executor service is needed as we'll use single thread to merge");

lucene/core/src/test/org/apache/lucene/codecs/lucene99/TestLucene99HnswQuantizedVectorsFormat.java

@@ -220,9 +220,6 @@ public void testLimits() {
     expectThrows(
         IllegalArgumentException.class,
         () -> new Lucene99HnswScalarQuantizedVectorsFormat(20, 100, 0, 7, false, 0.8f, null));
-    expectThrows(
-        IllegalArgumentException.class,
-        () -> new Lucene99HnswScalarQuantizedVectorsFormat(20, 100, 100, 7, false, null, null));
     expectThrows(
         IllegalArgumentException.class,
         () ->