(RE-2368) Update for CentOS 7

We can now remove the bandaids because CentOS 7 has been officially
released. This consists of removing the bandaid files themselves and
updating the mocks to remove lingering patch code. We also have updated
the pe-el-mock-config template to pull from osmirror instead of yo.
This isn't actually a thing. I'm curious what will happen if we define the mock stub but never actually use it.