behat_data_generators::the_following_exist() is gone, long life?

This is a followup / regression of MDL-48024, where the behat_data_generators::the_following_exist() method was renamed to behat_data_generators::the_following_entities_exist().

The public behat step behind the method, in the other side, was kept the same ("Given the following xxxx exist:") aiming to keep it BC with any use in behat features.

But it seems that we should also be kept the old php method working because 3rd party code can use it within own/custom steps. All those uses (hopefully not many) will be now breaking because the method does not exist anymore.

Thanks to marina and pholden for finding and reporting the problem @ MDL-48024 !

So this is about to confirm and apply the needed measures to reduce the impact of the regressions as possible. Here there is a (complementary) list of possible actions, feel free to present alternative ideas, extra actions or plan:

1. inform in upgrade.txt and share it @ forums / chats... about the change
2. look for uses in pluginland and direct report to affected people
3. consider reintroducing the old function (wrapping the new one) in a deprecated way to both debug and allow things to continue working over the std deprecation period.
4. anything else...