toolchain: do not check largefile, wchar, IPv6 and locale for glibc toolchains

The check_glibc function contained checks to verify that the user had
properly enabled the largefile, IPv6, locale and wchar options, to
match how glibc is configured. This was useful when the support for
glibc external toolchains was introduced, but since then, we added the
BR2_TOOLCHAIN_USES_GLIBC symbol that automatically enables largefile,
IPv6, locale and wchar support when a glibc or eglibc external
toolchain is used. Therefore, many of the check_glibc checks are
useless now, so we can remove these.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>