[chirp_devel] [PATCH][BTECH] Improved and renamed the start of clone mode, fixes #3015

The _do_magic() procedure has been renamed and simplified, because the reference for the troublesome alpha radio was removed (and hence support for it), and we no longer need more than one magic per radio.

Also as this is a btech driver the common magic for the btechs is set as the default value for the main class.