timeout_tests: do not call sleep from test thread
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).

kjbracey-arm/mbed,andcor02/mbed-os,kjbracey-arm/mbed,andcor02/mbed-os,mbedmicro/mbed,mbedmicro/mbed,kjbracey-arm/mbed,andcor02/mbed-os,andcor02/mbed-os,andcor02/mbed-os,andcor02/mbed-os,kjbracey-arm/mbed,mbedmicro/mbed,mbedmicro/mbed,mbedmicro/mbed