Update softdeleteable-filter.rst

[gpetraroli]

update softdeleateble configuration example

I think the the configuration example is related to an older version.

[stof]

The example uses the expanded syntax (supporting multiple entity managers), while you switch it to the shortcut syntax (supporting only the default entity manager). But both are valid. and the documentation has a note after that code snippet about the short syntax, which would not make sense if the code snippet shows the short syntax and not the expanded syntax.

[gpetraroli]

thank you @stof