Subs shouldn't take a model as an argument

This also nullifies the need for SubMap

examples/fullscreen/main.go

@@ -55,7 +55,7 @@ func update(message tea.Msg, mdl tea.Model) (tea.Model, tea.Cmd) {
 
 func subscriptions(_ tea.Model) tea.Subs {
 	return tea.Subs{
-		"tick": func(_ tea.Model) tea.Msg {
+		"tick": func() tea.Msg {
 			time.Sleep(time.Second)
 			return tickMsg{}
 		},

examples/simple/main.go

@@ -59,7 +59,7 @@ func view(model tea.Model) string {
 // second, sends a tick, and then restarts.
 func subscriptions(_ tea.Model) tea.Subs {
 	return tea.Subs{
-		"tick": func(_ tea.Model) tea.Msg {
+		"tick": func() tea.Msg {
 			time.Sleep(time.Second)
 			return TickMsg{}
 		},

examples/views/main.go

@@ -58,12 +58,12 @@ func subscriptions(model tea.Model) tea.Subs {
 	}
 }
 
-func tick(model tea.Model) tea.Msg {
+func tick() tea.Msg {
 	time.Sleep(time.Second)
 	return tickMsg{}
 }
 
-func frame(model tea.Model) tea.Msg {
+func frame() tea.Msg {
 	time.Sleep(time.Second / 60)
 	return frameMsg{}
 }

tea.go

@@ -32,17 +32,7 @@ func Batch(cmds ...Cmd) Cmd {
 // Sub is an event subscription; generally a recurring IO operation. If it
 // returns nil it's considered a no-op, but there's really no reason to have
 // a nil subscription.
-type Sub func(Model) Msg
-
-// SubMap applies a given model as an argument to a given subscription.
-func SubMap(sub Sub, model Model) Sub {
-	if sub == nil {
-		return nil
-	}
-	return func(_ Model) Msg {
-		return sub(model)
-	}
-}
+type Sub func() Msg
 
 // Subs is a keyed set of subscriptions. The key should be a unique
 // identifier: two different subscriptions should not have the same key or
@@ -280,7 +270,7 @@ func (p *Program) processSubs(msgs chan Msg, model Model, activeSubs subManager)
 						select {
 						case <-done:
 							return
-						case msgs <- s(model):
+						case msgs <- s():
 							continue
 						}
 					}