All the setup/teardown/pre/post/conditions template methods
now are required to return void. This was warned with phpunit 7
and now is enforced.

At the same time, fix a few wrong function names,
provider data and param types, return statements...

This makes everything to break, but it's what we'll be fixing
in the next commits, heh. :-)

Generated with php72 (min version supported), following the
instructions @ https://docs.moodle.org/dev/Composer

* Deprecated serialise_tool_proxy() as no longer used.
* Use tool_proxy_return_structure for each proxy.
* Added tests for getting all proxies and orphaned proxies.

The remove_course_contents function did not delete data from
course_module_completion table in most cases, resulting in large
quantities of orphaned data.

The new API works on normal databases (by deleting data based on the
subquery) and also on MySQL (by deleting the data using a weird join
on the subquery).