Revert "[Deviantart] [#1776] Remove the "you need session cookies to download mature scraps" warning (#1777)"

This reverts commit 1f02878351.

Mature scraps do yet again require cookies.

gallery_dl/extractor/deviantart.py

@@ -960,9 +960,15 @@ class DeviantartScrapsExtractor(DeviantartExtractor):
     )
     cookiedomain = ".deviantart.com"
     cookienames = ("auth", "auth_secure", "userinfo")
+    _warning = True
 
     def deviations(self):
         eclipse_api = DeviantartEclipseAPI(self)
+        if self._warning:
+            DeviantartScrapsExtractor._warning = False
+            if not self._check_cookies(self.cookienames):
+                self.log.warning(
+                    "No session cookies set: Unable to fetch mature scraps.")
 
         for obj in eclipse_api.gallery_scraps(self.user, self.offset):
             deviation = obj["deviation"]