Fix UnifiedPush info (#460)

Author: p1gp1g

src/data/signatures.yaml

@@ -458,12 +458,11 @@
   social-bluesky: "https://bsky.app/profile/tuta.com"
   social-x: "https://x.com/TutaPrivacy"
   social-linkedin: "https://linkedin.com/company/tutanota"
-- organization: "Unified Push"
+- organization: "UnifiedPush"
   url: "unifiedpush.org"
-  poc: "Simon <mail@sgougeon.fr>"
+  poc: "Simon <contact@unifiedpush.org>"
   region: "FR"
   social-mastodon: "https://fosstodon.org/@unifiedpush"
-  social-x: "https://x.com/UnifiedPush"
 - organization: "VideoLAN"
   url: "videolan.org"
   poc: "Nicolas POMEPUY <npomepuy.videolabs@gmail.com>"