Revert "Round-robin requests across connections"

This wasn't really needed. The connection index is kept in the index, so
properly round-robins over time.

The bug that led me to suspect this as an issue (the last node in the node
list not receiving any direct requests) was actually a connection retry issue,
likely fixed by 19dca3c90eb.

This reverts commit 476811163edc4d5f477e4ccd3d1593ed30b6835a.