Remove obsolete file common/xen-install.xml

Change I3e0f03ac42c39a2ed3fed2d530beb61f6b81873c renamed
xen-install.xml to section_xen-install.xml but forgot to remove the
now obsolete file.

Change-Id: I4b79d87da8cdb398ca9f0bdc967a029c6135e56d