vdso/ia32: Don't unmap rt-vdso

Found with fault-injected jump trampolines in vdso,
that on ia32 tests rt-vdso got unmapped.
I've fixed it previously, but have forgot it during
debugging vdso cleanup.

Fixes: commit 8544895a ("ia32/restorer: move 32-bit pie unmap to x86")
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>