Revert unintended docstring change.

Author: ajjackson

janus_core/cli/geomopt.py

@@ -216,7 +216,7 @@ def geomopt(
         Name of filter from ase.filters to wrap around atoms. If using
         --opt-cell-lengths or --opt-cell-fully, defaults to `FrechetCellFilter`.
     filter_func
-        Deprecated. Please use --filter.
+        Deprecated. Please use `--filter_class`.
     constraint_func
         Name of constraint function from ase.constraints, to apply constraints
         to atoms. Parameters should be included as a "constraint_kwargs" dict