Remove "library" variable from standalone.gypi.

BUG=111541
R=jkummerow@chromium.org

Signed-off-by: Thiago Farina <tfarina@chromium.org>

Review URL: https://codereview.chromium.org/12379082
Patch from Thiago Farina <tfarina@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13821 ce2b1a6d-e550-0410-aec6-3dcde31c8c00