Questionable ping logic in LogicalRepApplyLoop

While playing around with clang's scan-build I noticed this warning:

worker.c:2281:7: warning: Value stored to 'ping_sent' is never read
                                                ping_sent = true;
                                                ^           ~~~~

At first I thought it was a harmless unnecessary update, but looking
closer I wonder whether it isn't telling us there is a logic bug here.
Specifically, I wonder why the "ping_sent" variable is local to the
loop starting at line 2084, rather than having the same lifespan as
"last_recv_timestamp".  Do we really want to forget that we sent a
ping anytime we have to wait for more data?

In fact, looking closer, it appears to me that

(1) The "ping_sent = false" at line 2124 is also dead code, because
ping_sent could never be anything but false at this point;

(2) The "if (!ping_sent)" at line 2274 is also dead code, because
ping_sent is still never anything but false at that point.

In short, we could remove the ping_sent variable entirely without
changing this code's behavior.  I'm not 100% sure what semantics
it's trying to achieve, but I don't think it's achieving them.

			regards, tom lane