cluster/main: Remove extra @if ( Cluster::is_enabled() )

These have been discussed in the context of "@if &analyze" [1] and
am much in favor for not disabling/removing ~100 lines (more than
fits on a single terminal) out from the middle of a file. There's no
performance impact for having these handlers enabled unconditionally.
Also, any future work on "@if &analyze" will look at them again which
we could also skip.

This also reverts back to the behavior where the Cluster::LOG stream
is created even in non cluster setups like in previous Zeek versions.
As long as no one writes to it there's essentially no difference. If
someone does write to Cluster::LOG, I'd argue not black holing these
messages is better. Schema generators using Log::active_streams will
continue to discover Cluster::LOG even if they run in non-cluster
mode.

https://github.com/zeek/zeek/pull/3062#discussion_r1200498905

scripts/base/frameworks/cluster/main.zeek

@@ -347,8 +347,6 @@ function nodeid_topic(id: string): string
 	return nodeid_topic_prefix + id + "/";
 	}
 
-@if ( Cluster::is_enabled() )
-
 event Cluster::hello(name: string, id: string) &priority=10
 	{
 	if ( name !in nodes )
@@ -423,8 +421,6 @@ event zeek_init() &priority=5
 	Log::create_stream(Cluster::LOG, [$columns=Info, $path="cluster", $policy=log_policy]);
 	}
 
-@endif
-
 function create_store(name: string, persistent: bool &default=F): Cluster::StoreInfo
 	{
 	local info = stores[name];