arch: remove HAVE_COPY_THREAD_TLS

arch: remove HAVE_COPY_THREAD_TLS

All architectures support copy_thread_tls() now, so remove the legacy
copy_thread() function and the HAVE_COPY_THREAD_TLS config option. Everyone
uses the same process creation calling convention based on
copy_thread_tls() and struct kernel_clone_args. This will make it easier to
maintain the core process creation code under kernel/, simplifies the
callpaths and makes the identical for all architectures.

Cc: [email protected]
Acked-by: Thomas Bogendoerfer <[email protected]>
Acked-by: Greentime Hu <[email protected]>
Acked-by: Geert Uytterhoeven <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>