gst-plugins-good fixes: x11 and flac

gst-plugins-good's configure script expects the `ogg` package when building support for `flac`, which isn't pulled in if `flac` is requested. This PR fixes this.

Also, seems like X11 unconditional dependency isn't required and X11 will be pulled by separately enabled options.

Splitting this in two commits to ease reverting or bisecting just in case.