MT#56739 Remove already deprecated preference 'enable_t38'

The 'enable_t38' preference was added long time ago to
provision of phones that support fax services with t38.
We don't support those devices since long time.
Additionally the preference creates confusion with real
subscriber feature of enable t38 for mailtofax/faxtomail
service.

Due to those reason the preference can be removed.

Change-Id: I05b0f353eff9dcc6d57f51c6a32a6756f692d29d

db_scripts/diff/15753.down

@@ -0,0 +1,26 @@
+USE provisioning;
+SET autocommit=0;
+
+SELECT id INTO @pgid FROM voip_preference_groups WHERE name = 'Cloud PBX';
+
+INSERT INTO voip_preferences SET
+    voip_preference_groups_id = @pgid,
+    attribute = "enable_t38",
+    label = "Enable T38 Fax-over-IP",
+    type = 1,
+    max_occur = 1,
+    usr_pref = 1,
+    prof_pref = 0,
+    dom_pref = 0,
+    peer_pref = 0,
+    contract_pref = 0,
+    contract_location_pref = 0,
+    modify_timestamp = now(),
+    internal = 0,
+    expose_to_customer = 1,
+    expose_to_subscriber = 1,
+    data_type = 'boolean',
+    read_only = 0,
+    description = 'Enable T38 Fax-over-IP via auto-provisioning if the end device supports it.';
+
+COMMIT;

db_scripts/diff/15753.up

@@ -0,0 +1,8 @@
+USE provisioning;
+SET autocommit=0;
+
+DELETE FROM voip_preferences WHERE attribute = 'enable_t38';
+
+DELETE FROM kamailio.usr_preferences WHERE attribute='enable_t38';
+
+COMMIT;