[0.14.0.x] Remove check for mempool size in CInstantSendManager::CheckCanLock (#3119)
[0.14.0.x] Remove check for mempool size in CInstantSendManager::CheckCanLock (#3119)

* Remove check for mempool size in CInstantSendManager::CheckCanLock

This should not have been here at all and is already removed in develop.
Recent InstantSend failures on mainnet were partly related to this check.

* Skip autois tests for new IS system

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