Got rid of the "Invalid" state parameter

It was a bit too niche to be a state parameter

default/theme/default.go

@@ -199,12 +199,10 @@ func (Default) Pattern (id tomo.Pattern, state tomo.State, c tomo.Case) artist.P
 	offset := 0; switch {
 	case state.Disabled:                 offset = 1
 	case state.Pressed && state.On:      offset = 4
-	case state.Focused && state.On:      offset = 7
-	case state.Invalid && state.On:      offset = 8
+	case state.Focused && state.On:      offset = 6
 	case state.On:                       offset = 2
 	case state.Pressed:                  offset = 3
 	case state.Focused:                  offset = 5
-	case state.Invalid:                  offset = 6
 	}
 
 	switch id {

theme.go

@@ -371,12 +371,6 @@ type State struct {
 	// pattern is locked and cannot be interacted with. Disabled variations
 	// of patterns are typically flattened and greyed-out.
 	Disabled bool
-
-	// Invalid should be set to true if th element that is using this
-	// pattern wants to warn the user of an invalid interaction or data
-	// entry. Invalid variations typically have some sort of reddish tint
-	// or outline.
-	Invalid bool
 }
 
 // FontStyle specifies stylistic alterations to a font face.