remove '&' from URL patterns

'/?&#' -> '/?#' and '?&#' -> '?#'

According to https://www.ietf.org/rfc/rfc3986.txt, URLs are
"organized hierarchically" by using "the slash ("/"), question
mark ("?"), and number sign ("#") characters to delimit components"

gallery_dl/extractor/slideshare.py

@@ -20,7 +20,7 @@ class SlidesharePresentationExtractor(Extractor):
     filename_fmt = "{presentation}-{num:>02}.{extension}"
     archive_fmt = "{presentation}_{num}"
     pattern = (r"(?:https?://)?(?:www\.)?slideshare\.net"
-               r"/(?:mobile/)?([^/?&#]+)/([^/?&#]+)")
+               r"/(?:mobile/)?([^/?#]+)/([^/?#]+)")
     test = (
         (("https://www.slideshare.net"
           "/Slideshare/get-started-with-slide-share"), {