This should be applied only if the given FlowBlock has 0 or 1 outputs. If there is an output FlowBlock, all incoming edges to the given FlowBlock are moved so they flow into the output FlowBlock, then all remaining edges into or out of the given FlowBlock are removed. The given FlowBlock is \b not removed from \b this. This routine doesn't preserve loopedge information \param bl is the given Flow
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