meta/fiximports: clearer if statement

Prefer 'if x not in y' to 'if not x in y'.

Test Plan:
$ ./precommit.sh
phl: ws fix, 2 empty lines before license text
PEP8: all comments should start with a space

Conform to the PEP8 by updating all comments starting '#-' to '# -', and
all '#=' to '# ='.

This only affects the legal notices at the end of source files and the
boiler plates for test plans.

Test Plan:
$ ./precommit.sh
$ ./testbed/arcyd/acceptance_tests.sh
$ ./testbed/arcyon/acceptance_tests.sh