libc: remove now unneeded do_libc_headers

do_libc_headers is now a noop, and is no longer used, so remove that step.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 reporter_name="Harold Grovesteen"

 reporter_url="http://sourceware.org/ml/crossgcc/2009-11/msg00052.html"

 reporter_comment=""