[git commit prelink] libubacktrace: fix makefile clean target

[Carmelo Amoroso]

commit: http://git.uclibc.org/uClibc/commit/?id=c61993f7e0ad3a9014a4b73823faf1ba914f48a0
branch: http://git.uclibc.org/uClibc/commit/?id=refs/heads/prelink

Fix makefile lean target removing the old reference to the non
existing libubacktrace_ARCH_OUT variable.

Signed-off-by: Carmelo Amoroso <carmelo.amoroso at st.com>

Patch is too large, so refusing to show it