fix pillar get function when using salt-ssh

Since there were some changes in ``salt.modules.pillar.get`` (i.e. added ``merge`` and ``delimiter`` arg) it seems that this module (``salt.client.ssh.wrapper.pillar``) should also be updated to use the new form of ``get`` function while using salt via SSH (salt-ssh).

Without this fix, something like:
```
{% set pillar = salt['pillar.get']('mypillar', default={
  'foor': 'bar',
}, merge=True) %}
```
in a state file won't work, because the `` salt['pillar.get'] `` thing returns the "old" form of the function (the error is ``TypeError: get() got an unexpected keyword argument 'merge'``).

Notice that there are still some functions that differ from the ones in ``salt.modules.pillar`` module (e.g. ``ext`` and ``items`` are missing). Don't know what this means though.

This looks kinda serious to me. Also I think the whole ``salt.client.ssh.wrapper`` module was kinda "forgotten" (for example there are some serious differences between ``grains`` modules also).

I'm not sure but maybe this is also related to #16413?