remove duplicate indexes

[ayrat555]

pg hero found duplicate db indexes

Details
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On decompiled_smart_contractsdecompiled_smart_contracts_address_hash_index (address_hash)is covered byaddress_decompiler_version (address_hash, decompiler_version)
On staking_pools_delegatorsstaking_pools_delegators_delegator_address_hash_index (delegator_address_hash)is covered bypools_delegator_index (delegator_address_hash, pool_address_hash)
On transactionstransactions_to_address_hash_index (to_address_hash)is covered bytransactions_to_address_hash_recent_collated_index (to_address_hash, block_number DESC, index DESC, hash)

Changelog

• remove duplicate indexes

[vbaranov]

@ayrat555 could you find context where those indices have been introduced?

[ayrat555]

@vbaranov

1. https://github.com/poanetwork/blockscout/blob/master/apps/explorer/priv/repo/migrations/20190516140202_add_address_hash_index_to_decompiled_smart_contracts.exs (fix: add fields for contract filter performance #1966)
2. https://github.com/poanetwork/blockscout/blob/master/apps/explorer/priv/repo/migrations/20190523112839_create_staking_pools_delegators.exs#L17 (New tables for staking pools and delegators #2036)
3. https://github.com/poanetwork/blockscout/blob/master/apps/explorer/priv/repo/migrations/20190314084907_add_index_to_to_address_hash.exs (add incoming transactions count to contract view #1562)

[coveralls]

Pull Request Test Coverage Report for Build 9ae50a27-595b-487f-b4b4-b4b305d3dd69

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.09%) to 79.383%

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Totals
Change from base Build 966493d9-43a2-49bc-be70-770c5be1b661:	0.09%
Covered Lines:	5171
Relevant Lines:	6514

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💛 - Coveralls