We've decided to switch to PHPUnit 7 to make things easier. This also
means that we shouldn't suppress PHPUnit 8 warnings, otherwise we cannot
know if tests are already compatible with PHPUnit 8.
Note that the trait is not deleted, because it may still be necessary
for single tests -- we're just not including it by default. However, it
is now deprecated, and its use is discouraged.
Bug: T192167
Change-Id: If90e6b6ffe03dfb117ec2b4b13c79983fe1bd0f2
This is moved out of the main PHPUnit upgrade commit to allow
extensions to silence their warnings beforehand, to avoid breaking
their tests.
Bug: T192167
Change-Id: I60379a933a3a1b018d9f5ef6b51019002389dda3
