Remove the per-peer route tables (closes #122)

The routing table in memory now holds every route, so the two per-peer route
tables go, with every write, delete, count and read that served them. The
prefix handler applies each update to the table, writes the table's changes
every second, and stores each new prefix with its first-seen time. The peer
delete, its retry on the next flush and the updates held for it go too.

The image's memory settings fit a full table of about 1 GB: GOMEMLIMIT of
2.5 GiB, a 512 MiB page cache for the writing connection, and SQLite heap
limits of 768 MiB and 1 GiB. The README describes the new table, its
database copy and the memory budget.

Model: opus-5-5

internal/database/models.go

@@ -118,13 +118,6 @@ type IPInfo struct {
 	NeedsWHOISRefresh bool `json:"-"`
 }
 
-// LiveRouteDeletion represents parameters for deleting a live route
-type LiveRouteDeletion struct {
-	Prefix    string
-	PeerIP    string
-	IPVersion int
-}
-
 // SeenTimes is the earliest and the latest time one batch of updates saw an AS,
 // a peer or a peering. A row the batch adds is stored first seen at First and
 // last seen at Last. A row already stored takes First as its first_seen only