How to remove global “use strict” added by babel

As it has already been mentioned for Babel 6, it’s the transform-es2015-modules-commonjs preset which adds strict mode.
In case you want to use the whole es2015 preset without module transformations, put this in your .babelrc file:

{
  "presets": [
    ["es2015", { "modules": false }]
  ]
}

This will disable modules and strict mode, while keeping all other es2015 transformations enabled.