Remove duplicated enum Phase definition

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/material.h

@@ -27,6 +27,13 @@
 
 const int MaterialTableSize = 8192;
 
+/// Game phase
+enum Phase {
+  PHASE_ENDGAME = 0,
+  PHASE_MIDGAME = 128
+};
+
+
 /// MaterialInfo is a class which contains various information about a
 /// material configuration. It contains a material balance evaluation,
 /// a function pointer to a special endgame evaluation function (which in