timeout_tests: do not call sleep from test thread

This is up to scheduler to call sleep when threads are inactive.
So the thread should simply wait for the semaphore for ever (or test timeout).

Author: LMESTM

TESTS/mbed_drivers/timeout/timeout_tests.h

@@ -264,9 +264,7 @@ void test_sleep(void)
 
     bool deep_sleep_allowed = sleep_manager_can_deep_sleep_test_check();
     TEST_ASSERT_FALSE_MESSAGE(deep_sleep_allowed, "Deep sleep should be disallowed");
-    while (!sem.try_acquire()) {
-        sleep();
-    }
+    sem.wait();
     timer.stop();
 
     sleep_manager_unlock_deep_sleep();
@@ -323,9 +321,7 @@ void test_deepsleep(void)
 
     bool deep_sleep_allowed = sleep_manager_can_deep_sleep_test_check();
     TEST_ASSERT_TRUE_MESSAGE(deep_sleep_allowed, "Deep sleep should be allowed");
-    while (!sem.try_acquire()) {
-        sleep();
-    }
+    sem.wait();
     timer.stop();
 
     TEST_ASSERT_UINT64_WITHIN(delta_us, delay_us, timer.read_high_resolution_us());