Change the file name of the wal keys to match better

The other keys are stored in <oid>_keys so wal_keys fits better into
that pattern than the more redundant wal_encryption_keys where
"encryption" does not add any information but just makes the path
longer.

contrib/pg_tde/src/access/pg_tde_xlog_keys.c

@@ -22,7 +22,7 @@
 #endif
 
 #define PG_TDE_WAL_KEY_FILE_MAGIC 0x014B4557	/* version ID value = WEK 01 */
-#define PG_TDE_WAL_KEY_FILE_NAME "wal_encryption_keys"
+#define PG_TDE_WAL_KEY_FILE_NAME "wal_keys"
 
 #define MaxXLogRecPtr (~(XLogRecPtr)0)