Revert "fable wants to DIY a hash"

This reverts commit e1d96b932a.

overlay/batch/dispatch_bench_test.go

@@ -110,48 +110,3 @@ func BenchmarkDispatchSeedHeavy(b *testing.B) {
 	}
 	runDispatchBench(b, pkts, len(pkts))
 }
-
-// TestFlowKeyDigestDistinct pins digest quality: distinct flows must produce distinct keys across
-// a large sample, and the v4/v6 domains must not alias. Collisions are tolerated by construction
-// (headersMatch gates every merge), so this is a quality canary, not a correctness requirement.
-func TestFlowKeyDigestDistinct(t *testing.T) {
-	seen := make(map[flowKey]struct{}, 1<<17)
-	v4 := make([]byte, 40)
-	v4[0] = 0x45
-	v4[3] = 40 // total length
-	add := func(fk flowKey) {
-		if _, dup := seen[fk]; dup {
-			t.Fatal("flow digest collision in small sample")
-		}
-		seen[fk] = struct{}{}
-	}
-	var fk flowKey
-	for a := range 256 {
-		for b := range 128 {
-			v4[15] = byte(a) // src low byte
-			v4[19] = byte(b) // dst low byte
-			v4[21] = byte(a)
-			v4[23] = byte(b)
-			trimmed, ok := fk.parseIPv4Prologue(v4)
-			if !ok {
-				t.Fatal("v4 prologue rejected synthetic packet")
-			}
-			_ = trimmed
-			add(fk.withPorts(uint32(a)<<16 | uint32(b)))
-		}
-	}
-	v6 := make([]byte, 60)
-	v6[0] = 0x60
-	for a := range 256 {
-		for b := range 128 {
-			v6[23] = byte(a)
-			v6[39] = byte(b)
-			trimmed, ok := fk.parseIPv6Prologue(v6)
-			if !ok {
-				t.Fatal("v6 prologue rejected synthetic packet")
-			}
-			_ = trimmed
-			add(fk.withPorts(uint32(a)<<16 | uint32(b)))
-		}
-	}
-}