remove Glibc_vs_uClibc document

This document has nothing to do with Buildroot, and is probably a
leftover from the uClibc documentation.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
Acked-by: Luca Ceresoli <luca@lucaceresoli.net>
Acked-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>