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>

INSTALL

@@ -142,7 +142,6 @@ this detection and the sysv runlevel scripts have to be used.
 
 The old backend drivers are disabled because qdisk is now the default.
 This option can be used to build them anyway.
-  --enable-blktap1
   --enable-blktap2
 
 Build various stubom components, some are only example code. Its usually