Remove plugin-module related convenience methods

[bradjones1]

...from the membership provider manager. These are useful in my use case since I'm using plugin module, but it's not core functionality and membership no longer has any dependency on plugin.

My IDE shows this as a safe delete/refactor but looking for a review as matter of course.

[freelock]

Hmm I'm thinking this is useful in my case, too... going to review further in a couple hours

[bradjones1]

Think we can go ahead and remove these? I just moved the code to a site-specific module. While perhaps helpful, I don't think it belongs in Membership.

[freelock]

I did dig into the plugin system last week, and think I have my head around how it works, and where things go conceptually. But I'd really love to see how you're making use of this on your site-specific module.

I would tend to want things like this in the membership module, standard ways of finding/loading the plugin for a membership -- but if you have a better way that makes this all unnecessary, can you provide an example?