tests: drop redundant and slow `random` test
Suggested by @evelikov (!26 (comment 390066)):
Feel free to drop the random test altogether. It's an old public API no active users (pretty ancient code uses it) and the in-tree users drmSL and drmHash already have respective tests.
This test takes minutes to run, while all the other tests combined take barely more than a second.
Dropping it also helps the CI by avoiding random timeouts when random
takes more than the 4 minutes (!) we've allowed for it.