Remove duplicate `delete_by_query_rethrottle` method definition #537

Job	Run time
test-opensearch (2.5)	2m 27s
test-opensearch (2.6)	2m 31s
test-opensearch (2.7)	2m 25s
test-opensearch-faraday-1 (2.6)	2m 20s
test-opensearch (3.0)	2m 24s
test-opensearch-faraday-1 (2.7)	2m 13s
test-opensearch-security (2.5)	2m 13s
test-opensearch (3.1)	2m 4s
test-opensearch-faraday-1 (3.0)	1m 57s
test-opensearch-security (2.6)	2m 24s
test-opensearch (3.2)	2m 2s
test-opensearch-faraday-1 (3.1)	2m 0s
test-opensearch-faraday-1 (3.2)	2m 26s
test-opensearch (3.3)	2m 3s
test-opensearch-faraday-1 (3.3)	1m 57s
test-opensearch (jruby-9.3)	3m 0s
test-opensearch-security (2.7)	2m 15s
test-opensearch-faraday-1 (jruby-9.3)	2m 35s
test-opensearch-security (3.0)	1m 57s
test-opensearch-security (3.1)	2m 5s
test-opensearch-security (3.2)	2m 4s
test-opensearch-security (3.3)	2m 10s
test-opensearch-security (jruby-9.3)	1m 50s
	51m 22s

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