Remove unused files

These files don't appear to used by any SDK dependencies. From what I can tell sw_timer.c was just left over from /utilities in a previous version of KSDK. The 1.0.0 release doesn't provide this file.

fsl_interrupt_manager.c expects KSDK specific startup.c and linker script to be used which we don't. This is implemented differently in the mbed SDK

Previous tests past because the tests are ran linking against the release archive and not building the mbed SDK from source.

You can reproduce the online build failures by running:
python project.py -m K64F -p 25 -i uvision or python project.py -m K22F -p 25 -i uvision (once added) offline.