tools: Revert seabios and upstream qemu build changes

tools: Revert seabios and upstream qemu build changes

These have broken the build and it seems to be difficult to fix.  So
we will revert the whole lot for now, and await corrected patch(es).

Revert "fix the build when CONFIG_QEMU is specified by the user"
Revert "tools: fix permissions of git-checkout.sh"
Revert "scripts/git-checkout.sh: Is not bash specific. Invoke with /bin/sh."
Revert "Clone and build Seabios by default"
Revert "Clone and build upstream Qemu by default"
Revert "Rename ioemu-dir as qemu-xen-traditional-dir"
Revert "Move the ioemu-dir-find shell script to an external file"

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>