[Backport 2.x] Remove outdated default index mapping error message

[opensearch-trigger-bot]

Backport 2f7969a from #7008.

[github-actions]

Compatibility status:

Checks if related components are compatible with change b314a0c

Incompatible components

Skipped components

Compatible components

Compatible components: [https://github.com/opensearch-project/security.git, https://github.com/opensearch-project/alerting.git, https://github.com/opensearch-project/index-management.git, https://github.com/opensearch-project/anomaly-detection.git, https://github.com/opensearch-project/asynchronous-search.git, https://github.com/opensearch-project/sql.git, https://github.com/opensearch-project/observability.git, https://github.com/opensearch-project/common-utils.git, https://github.com/opensearch-project/job-scheduler.git, https://github.com/opensearch-project/reporting.git, https://github.com/opensearch-project/cross-cluster-replication.git, https://github.com/opensearch-project/k-nn.git, https://github.com/opensearch-project/security-analytics.git, https://github.com/opensearch-project/custom-codecs.git, https://github.com/opensearch-project/geospatial.git, https://github.com/opensearch-project/ml-commons.git, https://github.com/opensearch-project/performance-analyzer.git, https://github.com/opensearch-project/performance-analyzer-rca.git, https://github.com/opensearch-project/notifications.git, https://github.com/opensearch-project/neural-search.git]

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/25884/
• CommitID: b314a0c
  Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green.
  Is the failure a flaky test unrelated to your change?

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      1 org.opensearch.remotestore.SegmentReplicationUsingRemoteStoreIT.testPrimaryReceivesDocsDuringReplicaRecovery
      1 org.opensearch.remotestore.SegmentReplicationUsingRemoteStoreIT.testMultipleShards

• URL: https://build.ci.opensearch.org/job/gradle-check/25914/
• CommitID: b314a0c
  Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov]

Codecov Report

Merging #10130 (b314a0c) into 2.x (ad9355f) will increase coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##                2.x   #10130   +/-   ##
=========================================
  Coverage     70.83%   70.84%           
- Complexity    58250    58303   +53     
=========================================
  Files          4811     4811           
  Lines        275316   275316           
  Branches      40464    40464           
=========================================
+ Hits         195033   195049   +16     
- Misses        63576    63618   +42     
+ Partials      16707    16649   -58     

Files Changed	Coverage Δ
...ava/org/opensearch/index/mapper/MapperService.java	74.79% <ø> (ø)

... and 468 files with indirect coverage changes