Summary:
This diff renames all the stragglers in comments and strings from variations of "packager" to "Metro Bundler". I did one of three:
* Rename "packager" to "Metro Bundler"
* Rename "react-native-packager" to "Metro Bundler"
* Remove "packager" when code inside of Metro implies that it's about Metro
I also removed `Glossary.md` because it is unmaintained and very old. mjesun is currently starting to write documentation for Metro which will supersede whatever was there before.
Reviewed By: mjesun
Differential Revision: D5802993
fbshipit-source-id: ba99cb5ed04d84b0f7b7a8a0bf28ed99280a940a