Update communitybeats.asciidoc (elastic#8269) (elastic#8270)

Removing Cassandrabeat, as a link to it results in a 404: https://github.com/goomzee/cassandrabeat

(cherry picked from commit 07c1db6)

libbeat/docs/communitybeats.asciidoc

@@ -28,7 +28,6 @@ https://github.com/radoondas/apachebeat[apachebeat]:: Reads status from Apache H
 https://github.com/verticle-io/apexbeat[apexbeat]:: Extracts configurable contextual data and metrics from Java applications via the  http://toolkits.verticle.io[APEX] toolkit.
 https://github.com/goomzee/burrowbeat[burrowbeat]:: Monitors Kafka consumer lag using Burrow.
 https://github.com/hsngerami/hsnburrowbeat[hsnburrowbeat]:: Monitors Kafka consumer lag for Burrow V1.0.0(API V3).
-https://github.com/goomzee/cassandrabeat[cassandrabeat]:: Uses Cassandra's nodetool cfstats utility to monitor Cassandra database nodes and lag.
 https://github.com/hartfordfive/cloudflarebeat[cloudflarebeat]:: Indexes log entries from the Cloudflare Enterprise Log Share API.
 https://github.com/jarl-tornroos/cloudfrontbeat[cloudfrontbeat]:: Reads log events from Amazon Web Services https://aws.amazon.com/cloudfront/[CloudFront].
 https://github.com/aidan-/cloudtrailbeat[cloudtrailbeat]:: Reads events from Amazon Web Services' https://aws.amazon.com/cloudtrail/[CloudTrail].