Fix memory usage for event ordering changes

[EVODelavega]

Remove the tSubSlice map, which caused the race detector to complain, and was possibly the cause of a memory leak (unregistered subscribers for streams not being removed properly, and aggregating data that was never consumed).

[jeremyletang]

Only system tests are failing here. should we move forward?

[EVODelavega]

@jeremyletang Not sure why they're failing. I'll try to trigger the build again, but otherwise I think it's best to proceed. Preserving event order addresses a number of issues.

[jeremyletang]

@jeremyletang Not sure why they're failing. I'll try to trigger the build again, but otherwise I think it's best to proceed. Preserving event order addresses a number of issues.

From what @ashleyvega said it's normal that system test would fail for a while. just go ahead merging.

[ashleyvega]

@jeremyletang https://vegaprotocol.slack.com/archives/C9E6XA8GK/p1598624098220200

[ashleyvega]

PR description, please @EVODelavega.

[vega-ci-bot]

system-tests failed.

=== Test summary ===
../../grpcTesting/governance/newAssetTests.py .........x..........FFx... [ 89%]
s.s                                                                      [100%]
 testDeclinedBuiltinAssetDeposit 
 testPassedBuiltinAssetDeposit 
../../grpcTesting/governance/newMarketGovTests.py ....F..........FF....x [ 42%]
FFFF.......sFFFFFFFFF.FFF.F..F                                           [100%]
 testNewMarketRejectNoStake 
 testGetAllOfTheProposals[3] 
 testGetNewMarketProposals[3] 
 testNewMarketOpenSingleTok 
 testVoteYSmallHolder 
 testVoteYMediumNSmallHolder 
 testVoteTopUpSmallDuringVote 
 testVoteYOwnOpenProposal 
 testVoteYOpenProposal 
 testVoteNOpenProposal 
 testVoteNoStakeOpenProposal 
 testVoteNoStakeAddFunds 
 testVoteRejectProposal 
 testVotePassedProposal 
 testVoteBothYNOpen 
 testVoteTwiceYSameUser 
 testVoteEnactedMarket 
 testVoteDeclinedMarket 
 testVoteYTaintedKey 
 testSubmitEnactedGTCOrder 
 testVoteWithdrawAllDuringVote 
../../grpcTesting/governance/newMarketTradesTests.py FFFF.FEEFFFF        [100%]
 ERROR at setup of testCloseOutTraderBuyOrders 
 ERROR at setup of testCloseOutTraderSellOrders 
 testTradeGTCToGTC 
 testTradeGTTToGTT 
 testTradeGTCToIOC 
 testTradeGTCToFOK 
 testPositionsByParty 
 testTradesByMarket 
 testTradeGTTToIOC 
 testTradeGTTToFOK 
 testNoTradeGTCToStopped 
../../grpcTesting/margins/marginsTests.py x..x                           [100%]
../../grpcTesting/markets/marketsTests.py ...............                [100%]
../../grpcTesting/orders/amendOrdersTests.py .ssssssssssssssssssssssssss [ 81%]
ssssss                                                                   [100%]
../../grpcTesting/orders/cancelOrdersTests.py .....................s.s   [100%]
../../grpcTesting/orders/generalOrdersTests.py .............             [100%]
../../grpcTesting/orders/limitOrdersTests.py ............sF.             [100%]
 testWithdrawAllFilledGTTOrder 
../../grpcTesting/orders/marketOrdersTests.py ........                   [100%]
../../grpcTesting/orders/mixedOrdersTests.py ..................sss       [100%]
../../grpcTesting/orders/negativeOrdersTests.py ........................ [ 57%]
....F..ssssss.s...                                                       [100%]
 testNoFundsSubmitGTTOrderAddFunds 
../../grpcTesting/parties/partiesTests.py ..                             [100%]
../../grpcTesting/trading/positionsTests.py .X                           [100%]
../../grpcTesting/trading/tradesTests.py ..............                  [100%]
../../grpcTesting/wallet/walletTests.py ................................ [ 91%]
.s.                                                                      [100%]
../../rest/orders/negativeOrdersTests.py .                               [100%]