Remove resource size check.

[natefinch]

We can't be guaranteed to get content-length from the server, so it's
totally reasonable that we might not know the size. We do get the hash,
which is a better check anyway, so just ignore size.

QA Steps

1. juju deploy cs:~natefinch/starsay
2. Ensure it gets deployed fully
   (if the bug is not fixed, it'll never get past the install step)

[natefinch]

$$merge$$

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju