Close the CFP on the website

Seems like this never got removed after the CFP was closed?

Author: ericholscher

docs/_data/berlin-2025-config.yaml

@@ -219,7 +219,7 @@ sponsors:
 # Things that change over time, listed in order of change
 flaglanding: False
 flaghassponsors: True
-flagcfp: True
+flagcfp: False
 flagticketsonsale: True
 flagsoldout: False
 flagspeakersannounced: True