Remove (unnecessary) ember-inflector peer dependency

[kpfefferle]

When I install my project dependencies with Yarn, I get the following warning:

warning "ember-data@2.16.2" has unmet peer dependency "ember-inflector@^2.0.0".

It looks like the ember-inflector peer dependency was added to package.json back when it was a dev dependency. ember-inflector has since been upgraded to a direct dependency, so it no longer needs to be listed as a peer dependency as consuming applications get it automatically when they install ember-data.