Looks like the last reference to it was deleted in March 2018
(df7a660fb3).
Prior to that the last use was switched to go-cmp, which we've more
or-less standardized on, at this point.
I did this with a dumb editor macro, so some comments changed too.
Also rename root package from platform to influxdb.
In interest of minimizing risk, anyone importing the root package has
now aliased it to "platform" so that no changes beyond imports were
necessary in those files.
Lastly, replace the old platform module to local path /dev/null so that
nobody can accidentally reintroduce a platform dependency while
migrating platform code to influxdb.