hw: mcu: kinetis: clean commented out flash code
hw: mcu: kinetis: clean commented out flash code

Remove commented out code in kinetis_flash_write.

Signed-off-by: Fabio Utzig <66676b1ceaf93296e098708c09494361103aa635@apache.org>

mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core