Merge branch 'remove-duplicate-field-from-merge-request-type' into 'master'

Remove duplicate field from MergeRequestType

See merge request gitlab-org/gitlab-ce!25330

app/graphql/types/merge_request_type.rb

@@ -38,7 +38,6 @@ module Types
     field :should_be_rebased, GraphQL::BOOLEAN_TYPE, method: :should_be_rebased?, null: false
     field :rebase_commit_sha, GraphQL::STRING_TYPE, null: true
     field :rebase_in_progress, GraphQL::BOOLEAN_TYPE, method: :rebase_in_progress?, null: false
-    field :diff_head_sha, GraphQL::STRING_TYPE, null: true
     field :merge_commit_message, GraphQL::STRING_TYPE, method: :default_merge_commit_message, null: true, deprecation_reason: "Renamed to defaultMergeCommitMessage"
     field :default_merge_commit_message, GraphQL::STRING_TYPE, null: true
     field :merge_ongoing, GraphQL::BOOLEAN_TYPE, method: :merge_ongoing?, null: false