* remove dead code from Transifex
* use @vscode/l10n-dev for XLF operations for extensions
* generated files
* more generated files
* remove dead code
* move l10n-dev to where gulp is
* generated
Upgrades our build scripts to target ES2017 since they are run on modern versions of node
This allows us to remove shims for es6 features such as `Object.assign`, and also remove a few extra typings packages