remove unreferenced gyp_dummy.c 

The code that utilized this file was removed in r1184.

Review URL: https://codereview.chromium.org/142433002/
Patch from ericvw@gmail.com!


git-svn-id: http://gyp.googlecode.com/svn/trunk@1841 78cadc50-ecff-11dd-a971-7dbc132099af