Revert "stack/erp5: fix pandas version in erp5"

This reverts commit ca5ba490.

It's actually a good idea to update our pandas version (0.19.x is
already 7 years old, in one project we recently run into a bug of this
pandas version).

We only need to prepare erp5 with few changes so that it also support
those newer versions. This preperation was done in erp5!1738.

/reviewed-on !1355