This reverts commit
695860958a9a2e7c825bcec4d0d42b427f0fb47e.
The change introduced an introspection ABI break.
See also: https://bugzilla.gnome.org/show_bug.cgi?id=682125
If we want to move the parse() method to be a constructor or a class
method, we'll need to do more testing or add new API.
https://bugzilla.gnome.org/show_bug.cgi?id=754990
/**
* gdk_rgba_parse:
- * @rgba: (out): the #GdkRGBA to fill in
+ * @rgba: the #GdkRGBA to fill in
* @spec: the string specifying the color
*
* Parses a textual representation of a color, filling in