libc/uClibc: remove use of snapshots and specific date

We now have the ability to use a custom location, so supporting
snapshots or custom date is no longer needed. Let the user do the
required preparation in this case.

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

 reporter_name="Kevin Cernekee"

 reporter_url="http://sourceware.org/ml/crossgcc/2011-09/msg00037.html"

 reporter_comment="MIPS SDE-compatible toolchain"