Investigate pruning of eth signatures for batches

[jackzampolin]

It appears that eth signatures for batches aren't being pruned at the same time batches are being pruned:

$ sommelier q gravity batch-tx-ethereum-signatures 1 0xa670d7237398238de01267472c6f13e5b8010fd1
signatures:
- batch_nonce: "1"
  ethereum_signer: 0x091EA016C80e0D7f761Fc7Cb9Aeb171169c0dc79
  signature: Z/RhgiKxX/EWCSfBDWiUaCu94XKxextNY6H5w0YJBDBtQ0CdmU/KtM537OqFM/r5n6HBDnJlNpAJRMi1fqWPqRs=
  token_contract: 0xa670d7237398238de01267472c6f13e5b8010fd1
- batch_nonce: "1"
  ethereum_signer: 0xA61Ef7cF3d9A28a5a6f1ef4CFFC3d53792461ABd
  signature: 8K9i15vqH+Wu8V9H3Qe4hA1pn6pSYyN6Lgv/6dIO+yQyMvTq+babKe0lxRQFHpPmGQXDDTcbMJtRB9zm+Kd3FRs=
  token_contract: 0xa670d7237398238de01267472c6f13e5b8010fd1
- batch_nonce: "1"
  ethereum_signer: 0x09E8E999459728b20be51e8be9Eda6Ac04cB93EE
  signature: CkGp2zSIqBd8I3Xz8R3F9SQPGU0MAs/g2BhsyLL9m+RdS1Ec1nXbzlpw/uqyJLtmWV38sktQrv48R2Evysl05Rs=
  token_contract: 0xa670d7237398238de01267472c6f13e5b8010fd1
- batch_nonce: "1"
  ethereum_signer: 0x133C776f4321A94Da266aD5fb52f4D45224E033e
  signature: t1b4sWBQoRJXP1i/zP59NdhIWhYnps9ZaE4HORVdPqMKmDHOrmqGObTs1vbiQkTMk5lE7zImabFr0OyDh4v1lRs=
  token_contract: 0xa670d7237398238de01267472c6f13e5b8010fd1
- batch_nonce: "1"
  ethereum_signer: 0x5299d547188B9351aD7e479E1eb2343e45578072
  signature: ifk8u//VcvgRkkJx6Ke3XjfschdYzLpNwTDOUm3f67BgfxhqoqBKwlKwUkK2VoJtfWyWhvvfdszMPG1s1WXB3Rs=
  token_contract: 0xa670d7237398238de01267472c6f13e5b8010fd1
- batch_nonce: "1"
  ethereum_signer: 0xb369b35BCf48257f5cc0AD688350dAe80bbc994A
  signature: lwzijlb5+PHAfBU9fB6ZwLety46qXu8mfusqalVfa2V62McE0j5a2hIeTPmh5cCndc/QTITgyChPFx6Y0Z6BERs=
  token_contract: 0xa670d7237398238de01267472c6f13e5b8010fd1
- batch_nonce: "1"
  ethereum_signer: 0x87e454966552f7E5c675b7Ec5FDB3489b81c6c51
  signature: FVSTZqA6okL0BaFK8lbICgOIBzHFo2Fys521gE7Nb20Ex583mmfnDnGjSJQTEv8sh04r1v4/i9LJel+Ek3aCuRw=
  token_contract: 0xa670d7237398238de01267472c6f13e5b8010fd1
- batch_nonce: "1"
  ethereum_signer: 0xeBbb780845F68920a805f1D69aB4Af7d0eFC7DF5
  signature: A+xwGWeBwe1rfC9ESSnWdqFeHqdl/6EoGggTKWY69sYYXhapz1kH98up7jEuE8rXV64Nqw3lVNdzO2ouEWQ0gRs=
  token_contract: 0xa670d7237398238de01267472c6f13e5b8010fd1
- batch_nonce: "1"
  ethereum_signer: 0x21c1E236688fC78580371cAe42e0E22Fc9A9696F
  signature: HGal5H2oMIKvP9Z50/Mt+w/klzFr02FDZ18Z6GA7fkBPEe419BX+J2WqegJmcIFj3hes79hJRSYGMJMhfmrXxhs=
  token_contract: 0xa670d7237398238de01267472c6f13e5b8010fd1

and

$ sommelier q gravity batch-tx 1 0xa670d7237398238de01267472c6f13e5b8010fd1