micropython-lib is now a submodule, and the manifest compilation process
will ensure it is available, so manifests no longer need to check that it
is available.
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
The ntptime module was previously only included in the ESP8266 port. This
commit factors that module out into the extmod directory, makes it support
different epochs, and includes it in the rp2 port.