Remove one more arch-specific target name.

One more target had the architecture added to its name since r14209
originally landed and was missed when that change was reverted. Remove
the architecture from v8_libbase as well.

BUG=
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/334793004

Patch from Richard Coles <torne@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21836 ce2b1a6d-e550-0410-aec6-3dcde31c8c00