Merge #262

262: Remove `libtock_platform::allows`. r=hudson-ayers a=jrvanwhy

Tock 2.0 system calls do not need the types in `allows`. Now that I'm reworking `libtock_platform` to use Tock 2.0 system calls, we can get rid of the module.

Co-authored-by: Johnathan Van Why <jrvanwhy@google.com>