[babl] base: don't define and set unused variable

[Nils Philippsen <nphilipp src gnome org>]

commit f75d194d77401768654c4faa7bd66409510d97fe
Author: Nils Philippsen <nils redhat com>
Date:   Wed Apr 20 13:43:08 2011 +0200

    base: don't define and set unused variable
    
    otherwise gcc 4.6 would warn about it

 babl/base/model-gray.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)
---
diff --git a/babl/base/model-gray.c b/babl/base/model-gray.c
index e6b907c..5582c78 100644
--- 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 +