Revert "Bug 974918 - Update marionette-content-script to 0.0.4 r=julienw"

This reverts commit fbecf93cd139b92260cacd67e3df3b32da048304.
Bug 976152 - Move test-agent off of npm
Merge pull request #2 from gaye/bug-976152

Bug 976152 - Move test-agent off of npm r=kgrandon