remove HostRenderer memoisation
remove HostRenderer memoisation

since it was only introduced to because producing stats would hit the
renderer twice, which is no longer the case.

weaveworks/scope,weaveworks/scope,weaveworks/scope,kinvolk/scope,alban/scope,alban/scope,alban/scope,alban/scope,weaveworks/scope,alban/scope,kinvolk/scope,kinvolk/scope,weaveworks/scope,weaveworks/scope,alban/scope,kinvolk/scope,kinvolk/scope,kinvolk/scope