pixel-formats: Fix doxygen warnings about missing format

We already have documentation in header which conflicts with the one
the source code. Remove it entirely as it confuses user as well.

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>

libweston/pixel-formats.c

@@ -431,15 +431,6 @@ pixel_format_is_opaque(const struct pixel_format_info *info)
 	return !info->opaque_substitute;
 }
 
-/** Retrieve the opaque substitute for a pixel format
- *
- * If the given pixel format contains an alpha channel, look up an identical
- * pixel format except where the alpha channel is ignored, if such format
- * exists. Otherwise returns the passed in format as is.
- *
- * \param info a pixel_format_info already retrieved using pixel_format_get_info()
- *
- */
 WL_EXPORT const struct pixel_format_info *
 pixel_format_get_opaque_substitute(const struct pixel_format_info *info)
 {