Remove incorrect use of array_map( 'get_post' ) in posts_pre_query

[bamadesigner]

Found posts don't need to be mapped for posts_pre_query filter. This mapping is taken care of by the core query.

Fixes #520.

[danielbachhuber]

Thanks @bamadesigner!

I'll review this at depth when I have a moment in the next week or two. It seems like a substantial change, so I want to make sure I understand it fully. If you can, it would be great to have a couple of unit tests documenting the nature of the change.

[danielbachhuber]

As it turns out, the test suite didn't run on this PR and there were a whole host of explosions when it did 🙃

I've fixed things up with 2f312cf466e08ef3ba35f24fcd1ea16a05fd014d (#522 )

Thanks again for the PR!

[bamadesigner]

Thanks @danielbachhuber!