Deprecate support for running Spock Tests

[krmahadevan]

TestNG Version

Note: only the latest version is supported
7.6.1

The support to run Spock tests from within TestNG should be deprecated and removed soon.
Following are the reasons behind this:

1. TestNG currently supports only spock 1.x series (which uses the JUnit3 and JUnit4 way of executing them)
2. TestNG does not intend to support running JUnit5 tests because JUnit5 already has an engine that is capable of running TestNG tests.
3. Spock 2.x series now works with the JUnit5 engine and so a user can always make use of (2) to run both their TestNG tests as well as the spock tests.

[krmahadevan]

More context around this can be found in this and this discussion.