Remove duplicate definition of ImfHalf

--- cinepaint/lib/float16.h2
+++ cinepaint/lib/float16.h
@@ -45,9 +45,6 @@
 #else /* OpenEXR/Nvidia half float */
 
 #include "libhalf/cinepaint_half.h"
-typedef unsigned short ImfHalf;
-ImfHalf	ImfFloat2Half (float f);
-float	ImfHalf2Float (ImfHalf h);
 
 #define ONE_FLOAT16 15360
 #define HALF_FLOAT16 14336