io/pointer: delete Foremost priority

It wasn't used, and it's not clear that it is useful at all in its current
form. For example, a single control with multiple handler keys (say, one for
scrolling and one for clicking) will only receive priority Foremost for one of
them.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

io/pointer/doc.go

@@ -95,8 +95,8 @@ For multiple grabbing handlers, the foremost handler wins.
 Priorities
 
 Handlers know their position in a matching set of a pointer through
-event priorities. The Shared and Foremost priorities are for matching sets
-with multiple handlers; the Grabbed priority indicate exclusive access.
+event priorities. The Shared priority is for matching sets with
+multiple handlers; the Grabbed priority indicate exclusive access.
 
 Priorities are useful for deferred gesture matching.
 

io/pointer/pointer.go

@@ -112,9 +112,6 @@ const (
 	// Shared priority is for handlers that
 	// are part of a matching set larger than 1.
 	Shared Priority = iota
-	// Foremost is like Shared, but the handler is
-	// the foremost in the matching set.
-	Foremost
 	// Grabbed is used for matching sets of size 1.
 	Grabbed
 )
@@ -187,8 +184,6 @@ func (p Priority) String() string {
 	switch p {
 	case Shared:
 		return "Shared"
-	case Foremost:
-		return "Foremost"
 	case Grabbed:
 		return "Grabbed"
 	default: