[MINOR][SQL] Remove implemented functions from comments of 'HiveSessionCatalog.scala'

## What changes were proposed in this pull request?
This PR removes implemented functions from comments of `HiveSessionCatalog.scala`: `java_method`, `posexplode`, `str_to_map`.

## How was this patch tested?
Manual.

Author: Weiqing Yang <yangweiqing001@gmail.com>

Closes #14769 from Sherry302/cleanComment.

sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveSessionCatalog.scala

@@ -230,10 +230,8 @@ private[sql] class HiveSessionCatalog(
   // List of functions we are explicitly not supporting are:
   // compute_stats, context_ngrams, create_union,
   // current_user, ewah_bitmap, ewah_bitmap_and, ewah_bitmap_empty, ewah_bitmap_or, field,
-  // in_file, index, java_method,
-  // matchpath, ngrams, noop, noopstreaming, noopwithmap, noopwithmapstreaming,
-  // parse_url_tuple, posexplode, reflect2,
-  // str_to_map, windowingtablefunction.
+  // in_file, index, matchpath, ngrams, noop, noopstreaming, noopwithmap,
+  // noopwithmapstreaming, parse_url_tuple, reflect2, windowingtablefunction.
   private val hiveFunctions = Seq(
     "hash",
     "histogram_numeric",