gnu: qemu: Update to 2.4.0.1. Include fix for CVE-2015-6855.

* gnu/packages/patches/qemu-CVE-2015-3209.patch,
  gnu/packages/patches/qemu-CVE-2015-4037.patch,
  gnu/packages/patches/qemu-CVE-2015-4103.patch,
  gnu/packages/patches/qemu-CVE-2015-4104.patch,
  gnu/packages/patches/qemu-CVE-2015-4105.patch,
  gnu/packages/patches/qemu-CVE-2015-4106-pt1.patch,
  gnu/packages/patches/qemu-CVE-2015-4106-pt2.patch,
  gnu/packages/patches/qemu-CVE-2015-4106-pt3.patch,
  gnu/packages/patches/qemu-CVE-2015-4106-pt4.patch,
  gnu/packages/patches/qemu-CVE-2015-4106-pt5.patch,
  gnu/packages/patches/qemu-CVE-2015-4106-pt6.patch,
  gnu/packages/patches/qemu-CVE-2015-4106-pt7.patch,
  gnu/packages/patches/qemu-CVE-2015-4106-pt8.patch,
  gnu/packages/patches/qemu-CVE-2015-5745.patch: Delete files.
* gnu/packages/patches/qemu-CVE-2015-6855.patch: New file.
* gnu-system.am (dist_patch_DATA): Add the new patch and delete the old ones.
* gnu/packages/qemu.scm (qemu-headless): Update to 2.4.0.1.  Add the new patch
  and delete the old ones.