Remove explicit semaphore in tests

[lehins]

Due to a recent switch to hspec from tasty we no longer need to create an explicit lock in tests, since hspec supports sequential test execution.
This task is about removing this ugly locking mechanism from cardano-crypto-class test suite:

cardano-base/cardano-crypto-class/test/Main.hs

Lines 23 to 27 in 245d69d

	-- This lock is used to prevent tests that use mlocking from running
	-- concurrently. Concurrent execution of these tests can cause the testsuite
	-- to exhaust mlock quota; but each individual test on its own should be
	-- fine.
	mlockLock <- mkLock