remove VERSION_TYPES_PERMITTING_CONFLICT

lib/logstash/plugin_mixins/elasticsearch/common.rb

@@ -12,12 +12,6 @@ module Common
     DOC_SUCCESS_CODES = [200, 201]
     DOC_CONFLICT_CODE = 409
 
-    # When you use external versioning, you are communicating that you want
-    # to ignore conflicts. More obviously, since an external version is a
-    # constant part of the incoming document, we should not retry, as retrying
-    # will never succeed.
-    VERSION_TYPES_PERMITTING_CONFLICT = ["external", "external_gt", "external_gte"]
-
     # Perform some ES options validations and Build the HttpClient.
     # Note that this methods may sets the @user, @password, @hosts and @client ivars as a side effect.
     # @param license_checker [#appropriate_license?] An optional license checker that will be used by the Pool class.