Depedencies on Python2/3 cross support (such as six, past and future)
are removed as only Python3 is supported at this point. Fewer
external deps is a good thing.
Signed-off-by: Ben Leslie <benno@brkawy.com>
Signed-off-by: Ivan Velickovic <i.velickovic@unsw.edu.au>
This commit also converts our own copyright headers to directly use
SPDX, but leaves all other copyright header intact, only adding the
SPDX ident. As far as possible this commit also merges multiple
Data61 copyright statements/headers into one for consistency.
