pg_dumpall: simplify coding of dropDBs()

There's no need for a StringInfo when all you want is a string
being constructed in a single pass.

Author: Álvaro Herrera <alvherre@kurilemu.de>
Reported-by: Ranier Vilela <ranier.vf@gmail.com>
Reviewed-by: Yang Yuanzhuo <1197620467@qq.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Andrew Dunstan <andrew@dunslane.net>
Discussion: https://postgr.es/m/CAEudQAq2wyXZRdsh+wVHcOrungPU+_aQeQU12wbcgrmE0bQovA@mail.gmail.com

src/bin/pg_dump/pg_dumpall.c

@@ -1833,7 +1833,6 @@ dropDBs(PGconn *conn)
 	for (i = 0; i < PQntuples(res); i++)
 	{
 		char	   *dbname = PQgetvalue(res, i, 0);
-		PQExpBuffer delQry = createPQExpBuffer();
 
 		/*
 		 * Skip "postgres" and "template1"; dumpDatabases() will deal with
@@ -1846,15 +1845,14 @@ dropDBs(PGconn *conn)
 		{
 			if (archDumpFormat == archNull)
 			{
-				appendPQExpBuffer(delQry, "DROP DATABASE %s%s;\n",
-								  if_exists ? "IF EXISTS " : "",
-								  fmtId(dbname));
-				fprintf(OPF, "%s", delQry->data);
+				fprintf(OPF, "DROP DATABASE %s%s;\n",
+						if_exists ? "IF EXISTS " : "",
+						fmtId(dbname));
 			}
 			else
 			{
-				appendPQExpBuffer(delQry, "DROP DATABASE IF EXISTS %s;\n",
-								  fmtId(dbname));
+				char	   *stmt = psprintf("DROP DATABASE IF EXISTS %s;\n",
+											fmtId(dbname));
 
 				ArchiveEntry(fout,
 							 nilCatalogId,	/* catalog ID */
@@ -1862,10 +1860,9 @@ dropDBs(PGconn *conn)
 							 ARCHIVE_OPTS(.tag = psprintf("DATABASE %s", fmtId(dbname)),
 										  .description = "DROP_GLOBAL",
 										  .section = SECTION_PRE_DATA,
-										  .createStmt = delQry->data));
+										  .createStmt = stmt));
+				pg_free(stmt);
 			}
-
-			destroyPQExpBuffer(delQry);
 		}
 	}