Revert "all: keep UserProfiles a slice instead of a map for longer"

This reverts commit e5894aba42.

Breaks macOS/iOS build. Reverting per chat with Josh; he'll fix later today.

control/controlclient/direct.go

@@ -654,7 +654,7 @@ func (c *Direct) PollNetMap(ctx context.Context, maxPolls int, cb func(*NetworkM
 			Peers:        resp.Peers,
 			LocalPort:    localPort,
 			User:         resp.Node.User,
-			UserProfiles: resp.UserProfiles,
+			UserProfiles: make(map[tailcfg.UserID]tailcfg.UserProfile),
 			Domain:       resp.Domain,
 			DNS:          resp.DNSConfig,
 			Hostinfo:     resp.Node.Hostinfo,
@@ -662,6 +662,9 @@ func (c *Direct) PollNetMap(ctx context.Context, maxPolls int, cb func(*NetworkM
 			DERPMap:      lastDERPMap,
 			Debug:        resp.Debug,
 		}
+		for _, profile := range resp.UserProfiles {
+			nm.UserProfiles[profile.ID] = profile
+		}
 		if resp.Node.MachineAuthorized {
 			nm.MachineStatus = tailcfg.MachineAuthorized
 		} else {