rpc: remove debug logging

This was added recently, in #94778, and contributes to log spam of the
following sort:

I230404 15:00:33.826337 2400 rpc/context.go:2249  [T1,n1,rnode=2,raddr=127.0.0.1:55941,class=default,rpc] 268  connection heartbeat loop ended with err: <nil>
I230404 15:00:33.826338 3986 rpc/context.go:2249  [T1,n2,rnode=3,raddr=127.0.0.1:55955,class=system,rpc] 269  connection heartbeat loop ended with err: <nil>
I230404 15:00:33.826367 3455 rpc/context.go:2249  [T1,n2,rnode=3,raddr=127.0.0.1:55955,class=default,rpc] 270  connection heartbeat loop ended with err: <nil>
I230404 15:00:33.826394 3354 rpc/context.go:2249  [T1,n2,rnode=2,raddr=127.0.0.1:55941,class=default,rpc] 271  connection heartbeat loop ended with err: <nil>

Release note: None

pkg/rpc/context.go

@@ -2298,8 +2298,7 @@ func (rpcCtx *Context) grpcDialNodeInternal(
 			// Run the heartbeat; this will block until the connection breaks for
 			// whatever reason. We don't actually have to do anything with the error,
 			// so we ignore it.
-			err := rpcCtx.runHeartbeat(ctx, conn, target)
-			log.Infof(ctx, "connection heartbeat loop ended with err: %v", err)
+			_ = rpcCtx.runHeartbeat(ctx, conn, target)
 			maybeFatal(ctx, rpcCtx.m.Remove(k, conn))
 
 			// Context gets canceled on server shutdown, and if that's likely why