Revert 97987 - Switching NaCl IRT to be built inside the chrome build.

Revert 97987 - Switching NaCl IRT to be built inside the chrome build.

Fourth attempt:

Switching IRT to be built inside the chrome build. Dropping the IRT download
step from the DEPS. Step3 of a many step plan to switch where ppapi + irt
are built.
Dropping download_nacl_irt because we no longer rely on a prebuilt copy.
Dropping irt download drop source tarball (assume people using it will have
to download / build their own nacl toolchain).

Old Review URL: http://codereview.chromium.org/7669058
Review URL: http://codereview.chromium.org/7701017

TBR=bradnelson@google.com
Review URL: http://codereview.chromium.org/7701026

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@98030 0039d316-1c4b-4281-b951-d872f2087c98