In order for v1.19.1 to load a .mpy, the formerly-feature-flags which are
now used for the sub-version must be zero.
The sub-version is only used to indicate a native version change, so it
should be zero when emitting bytecode-only .mpy files.
This work was funded through GitHub Sponsors.
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>