examples: Reverting the serial lock solution

Reverting the serial lock solution for corrupted serial
prints on the terminal as the issue is only occurring with
ARMClang compiler with THREADX RTOS. So, using serial lock
for all combinations of compilers and RTOSes is not the
best solution. A better solution would be added in the
following commit.

Signed-off-by: Ahmed.Ismail <Ahmed.Ismail@arm.com>