Count distinct error message

Update count distinct error message for streaming datasets/dataframes to match current behavior. These aggregations are not yet supported.

Author: jtoka

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/UnsupportedOperationChecker.scala

@@ -103,9 +103,8 @@ object UnsupportedOperationChecker {
           }
           throwErrorIf(
             child.isStreaming && distinctAggExprs.nonEmpty,
-            "Distinct aggregations are not supported on streaming DataFrames/Datasets, unless " +
-              "it is on aggregated DataFrame/Dataset in Complete output mode. Consider using " +
-              "approximate distinct aggregation (e.g. approx_count_distinct() instead of count()).")
+            "Distinct aggregations are not supported on streaming DataFrames/Datasets. Consider " +
+              "using approx_count_distinct() instead.")
 
         case _: Command =>
           throwError("Commands like CreateTable*, AlterTable*, Show* are not supported with " +