Get rid of mw.loader.go and mw.loader.version

- loader#go: No longer required; never truly 'public'.
- loader#version: deprecated since 1.18.

No usage in the MediaWiki: NS on the Wikimedia cluster.

Change-Id: I57d340015621c8dd8dae57f9cbca05a03d44ee75
Merge "Get rid of mw.loader.go and mw.loader.version"