python3: fix build on Ubuntu/Debian multi-arch

python3: fix build on Ubuntu/Debian multi-arch

This issue was introduced after upgrading to 3.8.
Patch `006-remove-multi-arch-and-local-paths.patch` was dropped. It was
tested on x86, but when using the x86_64 compiler in OpenWrt, the issue is
present.

The issue seems to be about Ubuntu/Debian's multi-arch support in
Python/Python3 setup [which I forgot about]. The code runs it regardless of
whether it cross-compiles or not, and for OpenWrt, this causes issues, as
it introduces absolute include paths from the host system.

Fixes https://github.com/openwrt/packages/issues/10452

Fixes: 48277ec915815 ("python3: bump to version 3.8")
Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>