Remove unnecessary and deprecated VCAP_APPLICATION variables

[#84949358]
Use CURRENT_TIMESTAMP as the default value for created_at

* Mysql 5.6 on AWS RDS sets `--explicit_defaults_for_timestamp`, causing
  errors for created_at when no default value is set, this provides a
  sane default value, it should not change behavior as Sequel sends a
  value for created_at

[#78499982]
Send max_keys as a symbol, fog converts the key

[#80814826]
Remove app_soft_delete_destroyer initializer

[#81626602]