swrast: remove explicit size from texfetch_funcs array

By removing the array size, the static assertion to check for missing
elements can do its job properly.  This will catch cases where a new
Mesa format is added but the swrast texfetch code isn't updated.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/swrast/s_texfetch.c

@@ -115,7 +115,7 @@ static struct {
    FetchTexelFunc Fetch2D;
    FetchTexelFunc Fetch3D;
 }
-texfetch_funcs[MESA_FORMAT_COUNT] =
+texfetch_funcs[] =
 {
    {
       MESA_FORMAT_NONE,