AttributeImage : remove useless override

The previous code was removed in d5b0bb02, and until then the method was just calling the parent doing nothing more

core/attributedef.class.inc.php

@@ -7945,18 +7945,6 @@ class AttributeImage extends AttributeBlob
 		return "Image";
 	}
 
-	/**
-	 * {@inheritDoc}
-	 * @see AttributeBlob::MakeRealValue()
-	 */
-	public function MakeRealValue($proposedValue, $oHostObj)
-	{
-		$oDoc = parent::MakeRealValue($proposedValue, $oHostObj);
-
-		// The validation of the MIME Type is done by CheckFormat below
-		return $oDoc;
-	}
-
 	/**
 	 * Check that the supplied ormDocument actually contains an image
 	 * {@inheritDoc}