feat: Removed attach command and CLI option related to attach

* Card ID: CCT-425
* Removed attach command
* Removed --auto-attach and --autosubscribe CLI options of
  register command
* Removed --servicelevel CLI option of register command too,
  because this CLI option was possible to use only with
  --auto-attach CLI option. Thus, it does not make sense
  to keep this option
* Removed unit tests for attach command
* Modified unit tests for register command. Only SCA mode
  is considered.