Comment 9 for bug 1582515

I was never fond of strip and mentioned it while deciding it during the Budapest sprint so I all for deprecating this.

This is also the only case where we have a disconnect between the phase/step name and the directory it lands into.

Just for the record, from snapcraft 1.0 to 2.0 the rename was decided to be:

1.x 2.x
snap strip
assemble snap

And `snap` would take a dir to replace `snappy build`