Revert accidental change to pg_config_manual.h.

This was broken in commit 53dbc27c62, which
introduced unlogged tables.  Fortunately, as debugging tools go, this one
is pretty cheap, which is probably why it took nine months for someone to
notice, but it's not intended to be enabled by default, so revert.

Noted by Fujii Masao.

src/include/pg_config_manual.h

@@ -218,7 +218,7 @@
  * Enable debugging print statements for WAL-related operations; see
  * also the wal_debug GUC var.
  */
-#define WAL_DEBUG
+/* #define WAL_DEBUG */
 
 /*
  * Enable tracing of resource consumption during sort operations;