Event queue was using its own Timer or LowPowerTimer objects to derive
millisecond tick counts. This is unnecessary in RTOS builds, where the
RTOS is maintaining a tick count.

It also makes more sense to use the actual RTOS tick count, as the
values are being used to compute tick timeouts for RTOS calls. Computing
these RTOS tick delays with a separate timer could conceivably lead to
rounding errors.

Fixes: #5378