remove old seeding code

Old code created `Post` instances without an associated `User`.  The assumption is made in the rest of the app that all Posts have a User, so this is a problem. eg, the following code in a view:

```ruby
post.user.name
```

would end up throwing an exception:

```
NoMethodError: undefined method `name' for nil:NilClass
```
Merge pull request #1 from gadtfly/patch-1

remove old seeding code