Removed operations from master state when an agent is downgraded.
Removed operations from master state when an agent is downgraded.

When an agent is downgraded from one with the AGENT_OPERATION_FEEDBACK
capability to one without this capability, the master needs to remove
terminal-but-unACKed operations from its state which operate on agent
default resources, since the downgraded agent will not resend status
updates for these operations.

Review: https://reviews.apache.org/r/69876/

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