base: don't define and set unused variable

otherwise gcc 4.6 would warn about it

diff --git a/babl/base/model-gray.c b/babl/base/model-gray.c
index e6b907c4e273182619d56fd390183238584f6e4b..5582c782361cf17d608b57ef1504866cfe07aa49 100644 (file)
--- a/babl/base/model-gray.c
+++ b/babl/base/model-gray.c
@@ -143,12 +143,11 @@ rgba_to_gray (char *src,
   while (n--)
     {
       double red, green, blue;
-      double luminance, alpha;
+      double luminance;
 
       red   = ((double *) src)[0];
       green = ((double *) src)[1];
       blue  = ((double *) src)[2];
-      alpha = ((double *) src)[3];
 
       luminance = red * RGB_LUMINANCE_RED +
                   green * RGB_LUMINANCE_GREEN +