cosmetics(pgxn/neon): WP code small clean up (#11824)

## Problem
Some small cosmetic changes I made while reading the code. Should not
affect anything.

## Summary of changes
- Remove `n_votes` field because it's not used anymore
- Explicitly initialize `safekeepers_generation` with
`INVALID_GENERATION` if the generation is not present (the struct is
zero-initialized anyway, but the explicit initialization is better IMHO)
- Access SafekeeperId via pointer `sk_id` created above

pgxn/neon/neon_walreader.c

@@ -150,7 +150,7 @@ NeonWALReaderFree(NeonWALReader *state)
  * fetched from timeline 'tli'.
  *
  * Returns NEON_WALREAD_SUCCESS if succeeded, NEON_WALREAD_ERROR if an error
- * occurs, in which case 'err' has the desciption. Error always closes remote
+ * occurs, in which case 'err' has the description. Error always closes remote
  * connection, if there was any, so socket subscription should be removed.
  *
  * NEON_WALREAD_WOULDBLOCK means caller should obtain socket to wait for with

pgxn/neon/walproposer.c

@@ -124,6 +124,7 @@ WalProposerCreate(WalProposerConfig *config, walproposer_api api)
 	}
 	else
 	{
+		wp->safekeepers_generation = INVALID_GENERATION;
 		host = wp->config->safekeepers_list;
 	}
 	wp_log(LOG, "safekeepers_generation=%u", wp->safekeepers_generation);
@@ -756,7 +757,7 @@ UpdateMemberSafekeeperPtr(WalProposer *wp, Safekeeper *sk)
 	{
 		SafekeeperId *sk_id = &wp->mconf.members.m[i];
 
-		if (wp->mconf.members.m[i].node_id == sk->greetResponse.nodeId)
+		if (sk_id->node_id == sk->greetResponse.nodeId)
 		{
 			/*
 			 * If mconf or list of safekeepers to connect to changed (the
@@ -781,7 +782,7 @@ UpdateMemberSafekeeperPtr(WalProposer *wp, Safekeeper *sk)
 	{
 		SafekeeperId *sk_id = &wp->mconf.new_members.m[i];
 
-		if (wp->mconf.new_members.m[i].node_id == sk->greetResponse.nodeId)
+		if (sk_id->node_id == sk->greetResponse.nodeId)
 		{
 			if (wp->new_members_safekeepers[i] != NULL && wp->new_members_safekeepers[i] != sk)
 			{
@@ -1071,7 +1072,6 @@ RecvVoteResponse(Safekeeper *sk)
 	/* ready for elected message */
 	sk->state = SS_WAIT_ELECTED;
 
-	wp->n_votes++;
 	/* Are we already elected? */
 	if (wp->state == WPS_CAMPAIGN)
 	{

pgxn/neon/walproposer.h

@@ -845,9 +845,6 @@ typedef struct WalProposer
 	/* timeline globally starts at this LSN */
 	XLogRecPtr	timelineStartLsn;
 
-	/* number of votes collected from safekeepers */
-	int			n_votes;
-
 	/* number of successful connections over the lifetime of walproposer */
 	int			n_connected;