Reduce excessive dereferencing of function pointers

It is equivalent in ANSI C to write (*funcptr) () and funcptr().  These
two styles have been applied inconsistently.  After discussion, we'll
use the more verbose style for plain function pointer variables, to make
it clear that it's a variable, and the shorter style when the function
pointer is in a struct (s.func() or s->func()), because then it's clear
that it's not a plain function name, and otherwise the excessive
punctuation makes some of those invocations hard to read.

Discussion: https://www.postgresql.org/message-id/f52c16db-14ed-757d-4b48-7ef360b1631d@2ndquadrant.com

src/backend/commands/analyze.c

@@ -526,7 +526,7 @@ do_analyze_rel(Relation onerel, int options, VacuumParams *params,
 
 			stats->rows = rows;
 			stats->tupDesc = onerel->rd_att;
-			(*stats->compute_stats) (stats,
+			stats->compute_stats(stats,
 									 std_fetch_func,
 									 numrows,
 									 totalrows);
@@ -830,7 +830,7 @@ compute_index_stats(Relation onerel, double totalrows,
 				stats->exprvals = exprvals + i;
 				stats->exprnulls = exprnulls + i;
 				stats->rowstride = attr_cnt;
-				(*stats->compute_stats) (stats,
+				stats->compute_stats(stats,
 										 ind_fetch_func,
 										 numindexrows,
 										 totalindexrows);

src/backend/commands/portalcmds.c

@@ -397,7 +397,7 @@ PersistHoldablePortal(Portal portal)
 		/* Fetch the result set into the tuplestore */
 		ExecutorRun(queryDesc, ForwardScanDirection, 0L, false);
 
-		(*queryDesc->dest->rDestroy) (queryDesc->dest);
+		queryDesc->dest->rDestroy(queryDesc->dest);
 		queryDesc->dest = NULL;
 
 		/*

src/backend/commands/seclabel.c

@@ -122,7 +122,7 @@ ExecSecLabelStmt(SecLabelStmt *stmt)
 	}
 
 	/* Provider gets control here, may throw ERROR to veto new label. */
-	(*provider->hook) (&address, stmt->label);
+	provider->hook(&address, stmt->label);
 
 	/* Apply new label. */
 	SetSecurityLabel(&address, provider->provider_name, stmt->label);