tools: remove gyp test directory

gyp tests are not performed in iojs and it's size about 8M bytes. We
can check gyp tests outside of iojs and reduce the size of the
repository by removing them.

PR-URL: https://github.com/iojs/io.js/pull/1350


Reviewed-By: Johan Bergström <bugs@bergstroem.nu>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Rod Vagg <rod@vagg.org>