[libmediaart] Remove duplicate introspection comment for media_art_error_quark()

[Sam Thursfield <sthursfield src gnome org>]

commit 8ef56aab48f47e16ba297812b2eebfd8ac863d50
Author: Sam Thursfield <sam afuera me uk>
Date:   Fri Jul 21 13:42:01 2017 +0100

    Remove duplicate introspection comment for media_art_error_quark()
    
    Fixes this warning:
    
        libmediaart/extract.h:93: Warning: MediaArt: multiple comment blocks documenting 
'media_art_error_quark:' identifier (already seen at extract.c:1279).

 libmediaart/extract.h |    7 -------
 1 files changed, 0 insertions(+), 7 deletions(-)
---
diff --git a/libmediaart/extract.h b/libmediaart/extract.h
index c01d2cb..8f6440a 100644
--- a/libmediaart/extract.h
+++ b/libmediaart/extract.h
@@ -88,13 +88,6 @@ typedef enum {
 } MediaArtError;
 
 
-/**
- * media_art_error_quark:
- *
- * Returns: A #GQuark representing the type of #GError for #MediaArtProcess failures.
- *
- * Since: 0.2.0
- **/
 GQuark media_art_error_quark (void) G_GNUC_CONST;