Remove redundant variable pageSize in gistinitpage

In gistinitpage, pageSize variable looks redundant, instead just
pass BLCKSZ. This will be consistent with its peers BloomInitPage,
brin_page_init and SpGistInitPage.

Author: Bharath Rupireddy <bharath.rupireddy@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/flat/CALj2ACWj=V1k5591eeZK2sOg2FYuBUp6azFO8tMkBtGfXf8PMQ@mail.gmail.com

src/backend/access/gist/gistutil.c

@@ -756,9 +756,8 @@ void
 gistinitpage(Page page, uint32 f)
 {
 	GISTPageOpaque opaque;
-	Size		pageSize = BLCKSZ;
 
-	PageInit(page, pageSize, sizeof(GISTPageOpaqueData));
+	PageInit(page, BLCKSZ, sizeof(GISTPageOpaqueData));
 
 	opaque = GistPageGetOpaque(page);
 	opaque->rightlink = InvalidBlockNumber;