Feeds: Fix error parsing items with rights information

- 59afef6 added a duplicate assignment to item.rights that was putting
  a TextConstruct(!!!!) in the item JSON field instead of a string
- info.rights was being set to a TextConstruct (preexisting issue!)

chrome/content/zotero/xpcom/feedReader.js

@@ -82,7 +82,7 @@ Zotero.FeedReader = function (url) {
 		if (publisher) info.publisher = publisher;
 		
 		let rights = feed.rights;
-		if (rights) info.rights = rights;
+		if (rights) info.rights = rights.plainText();
 		
 		let issn = feed.issn;
 		if (issn) info.ISSN = issn;
@@ -489,9 +489,6 @@ Zotero.FeedReader._getFeedItem = function (feedEntry, feedInfo) {
 	let publisher = feedEntry.publisher;
 	if (publisher) item.publisher = publisher;
 	
-	let rights = feedEntry.rights;
-	if (rights) item.rights = rights;
-	
 	let language = feedEntry.language;
 	if (language) item.language = language;
 	

test/tests/data/feedArticleMetadata.rss

@@ -56,5 +56,6 @@
 	<prism:url>https://www.mdpi.com/2311-5521/9/6/120</prism:url>
 	
 	<cc:license rdf:resource="CC BY 4.0"/>
+	<dc:rights>Creative Commons Attribution (CC-BY)</dc:rights>
 </item>
 </rdf:RDF>