PE-241: drop the --platform option

This patch drops the --platform option since it only ever had
one possible argument value - AWS - which made it kind of useless.
PE-241: remove references to the --platform option from the tests

This patch removes referencs to the --platform option from the tests,
as the option has been removed.
Merge pull request #128 from mruzicka/PE-241_drop_platform_option

PE-241: drop the --platform option