Revert "nostrdb: close database when backgrounded"

This reverts commit da2bdad18d.

This commit was reverted because it was causing crashes (Occasional `EXC_BAD_ACCESS` errors when accessing database transactions), and because the push notification extension uses Ndb in a read-only manner, which means we no longer need these changes

Signed-off-by: Daniel D’Aquino <daniel@daquino.me>

nostrdb/NdbTxn.swift

@@ -29,14 +29,7 @@ class NdbTxn<T> {
             self.inherited = true
         } else {
             self.txn = ndb_txn()
-            let ok = ndb_begin_query(ndb.ndb.ndb, &self.txn) != 0
-            if !ok {
-                self.moved = false
-                self.txn = ndb_txn()
-                self.inherited = true
-                self.val = with(self)
-                return
-            }
+            let _ = ndb_begin_query(ndb.ndb.ndb, &self.txn)
             Thread.current.threadDictionary["ndb_txn"] = self.txn
             self.inherited = false
         }