tools: unhook blktap1 from the build and remove all references to it

tools: unhook blktap1 from the build and remove all references to it

This was disabled by default in Xen 4.4. Since xend has now been
removed from the tree I don't believe anything is using it.

We need to pass an explicit CONFIG_BLKTAP1=n to qemu-xen-traditional
otherwise it defaults to y and doesn't build.

This patch does all the ground work, the tools/blktap directory will
be removed in the next (*huge*) patch.

Note that this has no impact on blktap2, which is what libxl supports.
blktap1 was only usable via xend which has already been removed.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>