libelf: abolish libelf-relocate.c

libelf: abolish libelf-relocate.c

This file is not actually used.  It's not built in Xen's instance of
libelf; in libxc's it's built but nothing in it is called.  Do not
compile it in libxc, and delete it.

This reduces the amount of work we need to do in forthcoming patches
to libelf (particularly since as libelf-relocate.c is not used it is
probably full of bugs).

This is part of the fix to a security issue, XSA-55.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Chuck Anderson <chuck.anderson@oracle.com>