DevTools: Remove the concatenated_module_descriptors build target

The module descriptors concatenation has been moved into
the concatenate_application_code.py script. As a side effect,
this now produces proper descriptor sets for all applications.

R=dgozman, pfeldman

Review URL: https://codereview.chromium.org/605533006

git-svn-id: svn://svn.chromium.org/blink/trunk@182917 bbb929c8-8fbe-4397-9dbb-9b2b20218538