Revert "Fix for https://github.com/spark/core-firmware/issues/260 "delay(1) not as accurate as expected""

This reverts commit a1b5e185b86756a0bd6aa398d70254f3f96250c5.
Try #2 on fixing https://github.com/spark/core-firmware/issues/260

Uses DWT-CYCCNT as an additional timer base;  Will still block if there is a call to the Spark cloud, which could result in a longer than expected delay time for short (<10ms) delays