Remove unused field from the TDE file header

The userId field of the principal key info has never been used since
it was introduced in commit 210c95cf00
so we can safely remove it.

contrib/pg_tde/src/include/catalog/tde_principal_key.h

@@ -22,7 +22,6 @@
 typedef struct TDEPrincipalKeyInfo
 {
 	Oid			databaseId;
-	Oid			userId;
 	Oid			keyringId;
 	struct timeval creationTime;
 	char		name[PRINCIPAL_KEY_NAME_LEN];