[Remove] LegacyESVersion.V_7_6_* and V_7_7_* constants

[nknize]

Removes all usages of LegacyESVersion.V_7_6_ and LegacyESVersion.V_7_7_ version constants along with ancient API logic.

relates #2747

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/4952/
• CommitID: 166612b

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/4953/
• CommitID: bd98c64

[nknize]

Oh fun! Looks like we have a race condition in IndexShardIT.testIndexCanChangeCustomDataPath.

deleteReaderFiles must be getting called async before the test finishes copying.

[2022-10-19T08:21:35,640][ERROR][o.o.i.s.IndexShardIT     ] [testIndexCanChangeCustomDataPath] Failed to copy data path directory
java.nio.file.NoSuchFileException: /var/jenkins/workspace/gradle-check/search/server/build/testrun/internalClusterTest/temp/org.opensearch.index.shard.IndexShardIT_B9157C425F286EBE-001/rxeTWWtHeW/start-KZvCXclcHt/0/ipMqHwdkRym5TzwG0a3ubg/0/translog/translog-3794781907109570892.ckp

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: SUCCESS ✅
• URL: https://build.ci.opensearch.org/job/gradle-check/4991/
• CommitID: 7cd881f

[codecov-commenter]

Codecov Report

❌ Patch coverage is 68.58974% with 49 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.90%. Comparing base (db418fb) to head (2692841).
⚠️ Report is 3728 commits behind head on main.

Files with missing lines	Patch %	Lines
...g/opensearch/test/rest/OpenSearchRestTestCase.java	0.00%	14 Missing ⚠️
...ch/analysis/common/CommonAnalysisModulePlugin.java	0.00%	7 Missing and 1 partial ⚠️
.../node/reload/NodesReloadSecureSettingsRequest.java	0.00%	7 Missing ⚠️
...tion/admin/cluster/stats/ClusterStatsResponse.java	0.00%	6 Missing ⚠️
...on/admin/indices/forcemerge/ForceMergeRequest.java	20.00%	4 Missing ⚠️
...ateway/TransportNodesListGatewayStartedShards.java	40.00%	2 Missing and 1 partial ⚠️
...es/store/TransportNodesListShardStoreMetadata.java	40.00%	2 Missing and 1 partial ⚠️
...pensearch/cluster/metadata/AutoExpandReplicas.java	75.00%	0 Missing and 1 partial ⚠️
...org/opensearch/index/seqno/ReplicationTracker.java	50.00%	0 Missing and 1 partial ⚠️
...rg/opensearch/indices/analysis/AnalysisModule.java	0.00%	1 Missing ⚠️
... and 1 more

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #4837      +/-   ##
============================================
+ Coverage     70.87%   70.90%   +0.03%     
+ Complexity    57922    57884      -38     
============================================
  Files          4692     4692              
  Lines        276852   276648     -204     
  Branches      40236    40157      -79     
============================================
- Hits         196212   196151      -61     
+ Misses        64458    64314     -144     
- Partials      16182    16183       +1     

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[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/5115/
• CommitID: a317763

[dblock]

I believe this has been fixed in #4270, rebase?

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/5195/
• CommitID: 6bfadbb

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/6047/
• CommitID: 1f533a0
  Please examine the workflow log, locate, and copy-paste the failure below, then iterate to green.
  Is the failure a flaky test unrelated to your change?

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/6049/
• CommitID: 88f5daa
  Please examine the workflow log, locate, and copy-paste the failure below, then iterate to green.
  Is the failure a flaky test unrelated to your change?

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: SUCCESS ✅
• URL: https://build.ci.opensearch.org/job/gradle-check/6050/
• CommitID: 2692841