This babel plugin is intended to supress the deprecation warnings
from building plugins, however, discourse-plugins does not actually
consume this plugin at all. Currently this happens to work due to
how the babel worker processes are shared and the timing/ordering
of the build, but it will stop working with the embroider build.
This commit extracts the plugin the a shared package so that it
can be properly consumed by discourse-plugins as well as core.
Godfrey Chan