plugins: simplify shutdown loop, simply close the db

The only thing that needs ld->wallet after this is destroy_invoices_waiter (off jsonrpc)
Could not find any other destructors (destroy_*) that need wallet or db access after this.
Any db access would now segfault.

wallet/db.c

@@ -1276,7 +1276,6 @@ struct db *db_setup(const tal_t *ctx, struct lightningd *ld,
 	struct db *db = db_open(ctx, ld->wallet_dsn);
 	bool migrated;
 	db->log = new_log(db, ld->log_book, NULL, "database");
-	db->plugins_shutdown = &ld->plugins->shutdown;
 
 	db_begin_transaction(db);
 
@@ -2351,11 +2350,6 @@ void db_changes_add(struct db_stmt *stmt, const char * expanded)
 	tal_arr_expand(&db->changes, tal_strdup(db->changes, expanded));
 }
 
-void db_check_plugins_not_shutdown(struct db *db)
-{
-	assert(!*db->plugins_shutdown);
-}
-
 const char **db_changes(struct db *db)
 {
 	return db->changes;

wallet/db.h

@@ -249,9 +249,6 @@ struct db_stmt *db_prepare_v2_(const char *location, struct db *db,
 #define db_prepare_v2(db,query)						\
 	db_prepare_v2_(__FILE__ ":" stringify(__LINE__), db, query)
 
-/* Check that plugins are not shutting down when calling db_write hook */
-void db_check_plugins_not_shutdown(struct db *db);
-
 /**
  * Access pending changes that have been added to the current transaction.
  */

wallet/db_common.h

@@ -34,9 +34,6 @@ struct db {
 	 * Used to bump the data_version in the DB.*/
 	bool dirty;
 
-	/* Only needed to check shutdown state of plugins */
-	const bool *plugins_shutdown;
-
 	/* The current DB version we expect to update if changes are
 	 * committed. */
 	u32 data_version;