This should shave down bundle sizes by 14.4 kb for many non-blaze projects.
The other core meteor packages have not depended on `underscore` since #9362. However, we are only able to remove this last dependency now due to the previous commit, which eliminated usages of `underscore` from apps that did not have the package listed in their `packages` files. This was causing CI test failures that now should be corrected.
Any meteor apps currently using `_` without `underscore` listed in their `packages` file will need to add the package explicitly.
Version number of `meteor-base` bumped from 1.3.0 to 1.4.0.
There are only a few uses of `underscore` in these apps, and two of them actually used `underscore` without having it explicitly listed in their `packages` file.
This is a problem, because the apps were relying on the dependency from `meteor-base`, which we want to remove to cut down bundle sizes.
For the `modules` test app, I've added `underscore` to the `packages` file, because it is using `_` in an assertion about the module system. For the other app and all other uses of `_`, rather than add `underscore` to the `packages` files, I took the modernization route and replaced the functions with their ES6 equivalents, and then removed `underscore` from all `packages` files.
