internals: properly remove all docs

Part of the installed doc was not removed (if configured to).

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
(transplanted from cb0f625b3f9f704140aaeed024baac05e6b27df0)

# Compute s390-specific values

CT_DoArchTupleValues() {

    # That's the only thing to override

    if [ "${CT_ARCH_64}" = "y" ]; then

        CT_TARGET_ARCH="s390x"

    fi

}