Move isXMLMediaType to atom.go

entry.go

@@ -59,10 +59,6 @@ func alternateRelExists(l []*Link) bool {
 	return false
 }
 
-func isXMLMediaType(mediaType string) bool {
-	return strings.HasSuffix(mediaType, "/xml") || strings.HasSuffix(mediaType, "+xml")
-}
-
 func (e *Entry) AddExtension(name string, value any) {
 	e.Extensions = append(e.Extensions, &ExtensionElement{XMLName: xml.Name{Local: name}, Value: value})
 }