Remove kernel version check

Remove kernel version check

The kernel version check is used to avoid glibc to run on older
kernels where some syscall are not available and fallback code are
not enabled to handle graciously fail.  However, it does not prevent
if the kernel does not correctly advertise its version through
vDSO note, uname or procfs.

Also kernel version checks are sometime not desirable by users,
where they want to deploy on different system with different kernel
version knowing the minimum set of syscall is always presented on
such systems.

The kernel version check has been removed along with the
LD_ASSUME_KERNEL environment variable.  The minimum kernel used to
built glibc is still provided through NT_GNU_ABI_TAG ELF note and
also printed when libc.so is issued.

Checked on x86_64-linux-gnu.