[CHORE] One CHANGELOG entry, and drop a comment about another PR

Two CHANGELOG bullets pointed at this PR and said the same thing twice. The
first names what the exporter now decides success from, so the second goes.

The fixture comment described how this file and #4331 would be reconciled. That
is coordination between PRs, not something a reader of this file needs.

Signed-off-by: thc1006 <84045975+thc1006@users.noreply.github.com>

Author: thc1006

CHANGELOG.md

@@ -168,9 +168,6 @@ Increment the:
   errors flag, and one acknowledgement per record that names its target index
   and says the operation applied
   [#4297](https://github.com/open-telemetry/opentelemetry-cpp/pull/4297)
-* [BUG] Stop reading an Elasticsearch bulk response that only says the request
-  was accepted as a batch that was written
-  [#4297](https://github.com/open-telemetry/opentelemetry-cpp/pull/4297)
 
 * [BUG] Make SocketAddr string parsing safe and reject malformed addresses
   [#4292](https://github.com/open-telemetry/opentelemetry-cpp/pull/4292)

exporters/elasticsearch/test/es_log_record_exporter_test.cc

@@ -432,9 +432,6 @@ TEST(ElasticsearchBulkResponseTests, RejectsAnItemErrorUnderErrorsFalse)
 // that the status and the body actually reach it. A fake HTTP client drives the
 // callbacks from inside SendRequest(), which runs before Export() reaches the
 // wait, and the assertions are on the ExportResult.
-//
-// This fixture is the same one #4331 adds to this file. Whichever lands first,
-// the other drops the duplicate when it rebases.
 // ---------------------------------------------------------------------------
 namespace
 {