riscv64: remove mpers support

riscv64: remove mpers support

There is no riscv32 Linux support in Linux mainline,
and no compat support in riscv64 as well.

* linux/riscv64/arch_defs_.h: Remove.
* linux/riscv64/ioctls_arch1.h: Likewise.
* linux/riscv64/ioctls_inc1.h: Likewise.
* linux/riscv64/syscallent1.h: Likewise.
* Makefile.am (EXTRA_DIST): Remove them.
* configure.ac (st_MPERS([m32])): Remove riscv64.
* strace.1.in (.SH "MULTIPLE PERSONALITY SUPPORT"): Remove RISC-V
from the list.

Co-Authored-by: Dmitry V. Levin <ldv@altlinux.org>