TEST: testDocStats should always use forceMerge

Due to the recent change in LUCENE-8263, we need to adjust the deletion
ration to between 10% to 33% to preserve the current behavior of the
test. However, we may need another refinement if soft-deletes is enabled
as the actual deletes are different because of delete tombstones.

This commit prefers to always execute forceMerge instead of adjusting
the deletion ratio so that this test can focus on testing docStats.

Closes elastic#32449

server/src/test/java/org/elasticsearch/index/shard/IndexShardTests.java

@@ -2376,15 +2376,12 @@ public void testRecoverFromLocalShard() throws IOException {
         closeShards(sourceShard, targetShard);
     }
 
-    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/32449")
     public void testDocStats() throws IOException {
         IndexShard indexShard = null;
         try {
             indexShard = newStartedShard();
             final long numDocs = randomIntBetween(2, 32); // at least two documents so we have docs to delete
-            // Delete at least numDocs/10 documents otherwise the number of deleted docs will be below 10%
-            // and forceMerge will refuse to expunge deletes
-            final long numDocsToDelete = randomIntBetween((int) Math.ceil(Math.nextUp(numDocs / 10.0)), Math.toIntExact(numDocs));
+            final long numDocsToDelete = randomLongBetween(1, numDocs);
             for (int i = 0; i < numDocs; i++) {
                 final String id = Integer.toString(i);
                 indexDoc(indexShard, "_doc", id);
@@ -2434,7 +2431,6 @@ public void testDocStats() throws IOException {
 
             // merge them away
             final ForceMergeRequest forceMergeRequest = new ForceMergeRequest();
-            forceMergeRequest.onlyExpungeDeletes(randomBoolean());
             forceMergeRequest.maxNumSegments(1);
             indexShard.forceMerge(forceMergeRequest);