control/controlclient: remove Opts.KeepSharerAndUserSplit

It was added 2.5 years ago in c1dabd9436 but was never used.
Clearly that migration didn't matter.

We can attempt this again later if/when this matters.

Meanwhile this simplifies the code and thus makes working on other
current efforts in these parts of the code easier.

Updates #1909

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

control/controlclient/direct.go

@@ -74,7 +74,6 @@ type Direct struct {
 	discoPubKey           key.DiscoPublic
 	getMachinePrivKey     func() (key.MachinePrivate, error)
 	debugFlags            []string
-	keepSharerAndUserSplit bool
 	skipIPForwardingCheck bool
 	pinger                Pinger
 	popBrowser            func(url string)             // or nil
@@ -126,10 +125,6 @@ type Options struct {
 	// Status is called when there's a change in status.
 	Status func(Status)
 
-	// KeepSharerAndUserSplit controls whether the client
-	// understands Node.Sharer. If false, the Sharer is mapped to the User.
-	KeepSharerAndUserSplit bool
-
 	// SkipIPForwardingCheck declares that the host's IP
 	// forwarding works and should not be double-checked by the
 	// controlclient package.
@@ -255,7 +250,6 @@ func NewDirect(opts Options) (*Direct, error) {
 		authKey:               opts.AuthKey,
 		discoPubKey:           opts.DiscoPublicKey,
 		debugFlags:            opts.DebugFlags,
-		keepSharerAndUserSplit: opts.KeepSharerAndUserSplit,
 		netMon:                opts.NetMon,
 		skipIPForwardingCheck: opts.SkipIPForwardingCheck,
 		pinger:                opts.Pinger,
@@ -994,7 +988,6 @@ func (c *Direct) sendMapRequest(ctx context.Context, isStreaming bool, nu Netmap
 	sess.logf = c.logf
 	sess.vlogf = vlogf
 	sess.machinePubKey = machinePubKey
-	sess.keepSharerAndUserSplit = c.keepSharerAndUserSplit
 
 	// If allowStream, then the server will use an HTTP long poll to
 	// return incremental results. There is always one response right

control/controlclient/map.go

@@ -32,7 +32,6 @@ type mapSession struct {
 	logf           logger.Logf
 	vlogf          logger.Logf
 	machinePubKey  key.MachinePublic
-	keepSharerAndUserSplit bool // see Options.KeepSharerAndUserSplit
 
 	// Fields storing state over the course of multiple MapResponses.
 	lastNode               *tailcfg.Node
@@ -204,12 +203,8 @@ func (ms *mapSession) netmapForResponse(resp *tailcfg.MapResponse) *netmap.Netwo
 	for _, peer := range resp.Peers {
 		peer.InitDisplayNames(magicDNSSuffix)
 		if !peer.Sharer.IsZero() {
-			if ms.keepSharerAndUserSplit {
-				ms.addUserProfile(peer.Sharer)
-			} else {
 			peer.User = peer.Sharer
 		}
-		}
 		ms.addUserProfile(peer.User)
 	}
 	if DevKnob.ForceProxyDNS() {