remove the deprecated mark for all `actions_*` functions

The juju team returns to using `action-*` instead of `function-*`.
Based on this, it is necessary to undo mark for all functions `action_*`
(e.g. `action_set`) as deprecated and vice versa to mark the functions
`funcion_*` (e.g. `function_set`) as deprecated.

At the same time, it is necessary to maintain the functionality of both,
which will be best achieved in the same way as it is now done for the
`function_*` functions.

e.g.
```python
def action_get(key=None):
    """Gets the value of an action parameter, or all key/value param pairs"""
    cmd = ['action-get']
    # Fallback for older charms.
    if not cmd_exists('function-get'):
        cmd = ['function-get']
    ...
```