wgengine: remove unused singleflight group

Signed-off-by: James Tucker <james@tailscale.com>

wgengine/userspace.go

@@ -44,7 +44,6 @@ import (
 	"tailscale.com/util/clientmetric"
 	"tailscale.com/util/deephash"
 	"tailscale.com/util/mak"
-	"tailscale.com/util/singleflight"
 	"tailscale.com/version"
 	"tailscale.com/wgengine/filter"
 	"tailscale.com/wgengine/magicsock"
@@ -146,10 +145,6 @@ type userspaceEngine struct {
 	// value of the ICMP identifer and sequence number concatenated.
 	icmpEchoResponseCallback map[uint32]func()
 
-	// this singleflight is used to deduplicate calls to getStatus when we
-	// don't care if the data is perfectly fresh
-	getStatusSf singleflight.Group[struct{}, *Status]
-
 	// Lock ordering: magicsock.Conn.mu, wgLock, then mu.
 }