toolchain: remove installing twice in the "initial" subdir

toolchain: remove installing twice in the "initial" subdir

This was apparently introduced to recreate the toolchain (wipe
staging_dir/toolchain*, but keep build_dir/toolchain*, followed by a
`make toolchain/compile`).

But it leaves leftovers and causes re-links to happen at src_install phase,
because of the changed paths, possibly adding yet another source of issues.

With the prior commits removing various hacks related to the "initial"
folder we can remove installing it twice altogether.

The recreated toolchain is exactly the same as before.

Signed-off-by: Andre Heider <a.heider@gmail.com>