Remove the clone3 symbol from libc.a [BZ #31770]

clone3 isn't exported from glibc and is hidden in libc.so.  Fix BZ #31770
by removing clone3 alias.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>