Skip deep sleep test when running from US ticker
Skip deep sleep test when running from US ticker

Skip the systimer deep sleep test when running from the microsecond
ticker, since the microsecond ticker doesn't support operation in deep
sleep mode.

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