Remove incorrect assertion in CollapsingTopDocsCollectorSearchAfterTests

This assertion was simply wrong, but took time to catch as it was very rarely
triggered. The test already checks the correct assertion at an earlier time.

Fixes elastic#75736.

server/src/test/java/org/apache/lucene/grouping/CollapsingTopDocsCollectorSearchAfterTests.java

@@ -133,10 +133,11 @@ private <T extends Comparable<T>> void assertSearchCollapse(CollapsingDocValuesP
             currentValue = fieldDoc.fields[0];
         }
 
-        if (docsWithMissingField == false) {
-            assertEquals(expectedNumGroups, collapseTopFieldDocs.scoreDocs.length - 1);
-            assertEquals(topDocs.scoreDocs.length - 1, topDocsIndex);
+        for (; topDocsIndex < topDocs.scoreDocs.length; topDocsIndex++) {
+            FieldDoc fieldDoc = (FieldDoc) topDocs.scoreDocs[topDocsIndex];
+            assertEquals(fieldDoc.fields[0], currentValue);
         }
+
         w.close();
         reader.close();
         dir.close();