view: save memory by dropping smsg->{from_name} on use
We'll also save a few LoC when generating it. $smsg objects can
linger a while when rendering large threads, so saving a few
bytes here can add up to several hundred KB saved.
I noticed this while chasing the ref cycle leak in commit
b28e74c9dc0a (www: fix ref cycle from threading w/ extindex, 2021-10-03).
While there's no longer a leak, releasing memory earlier can
allow it to be reused sooner and reduce both memory traffic and
memory pressure.