glibc: remove version choice

glibc: remove version choice

We do not support uClibc-ng/musl C library version choice support,
do the same for GNU C Library.
No legacy handling required as only version choice is removed.

Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
[Thomas: move 3.2 kernel headers dependency to the libc choice in
toolchain/toolchain-buildroot/Config.in file, and added a Config.in
comment about it.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>