Bluetooth: Host: More bsim refactoring

Commit does the following changes:
* Use functionality from the `babbelkit` library for common functions
  related to flags, test progression (failing, passing etc.) and
  synchronization between two devices. Locally defined equivalents are
  removed.
* Removes the files containing only functionality that is provided
  by the `babblekit` library.
* Remove the `test_pre_init_f` and `test_tick_f` functions (commonly
  implemented as `test_init` and `test_tick`) from the modified tests.
  These functions are not needed as they were only used to fail the test
  if a device didn't complete the test within a certain time frame. This
  is already handled by the `sim_length` argument used in the test
  scripts.

Signed-off-by: Håvard Reierstad <haavard.reierstad@nordicsemi.no>