[iagno] Remove unused method.

[Arnaud B. <arnaudb src gnome org>]

commit f39057743e22051725f160387ada4218a84cc96e
Author: Arnaud Bonatti <arnaud bonatti gmail com>
Date:   Sat Sep 14 00:41:49 2019 +0200

    Remove unused method.

 src/game.vala | 6 ------
 1 file changed, 6 deletions(-)
---
diff --git a/src/game.vala b/src/game.vala
index 32e90dd..72c39bf 100644
--- a/src/game.vala
+++ b/src/game.vala
@@ -841,10 +841,4 @@ private enum Opening {
     ALTER_LEFT,
     ALTER_RIGHT,
     ALTER_BOTTOM;
-
-    internal static inline bool is_alter (Opening opening)
-    {
-        return opening != REVERSI
-            && opening != INVERTED;
-    }
 }