gnu: icecat: Update to 31.5.0.

gnu: icecat: Update to 31.5.0.

* gnu/packages/patches/icecat-CVE-2015-0822.patch,
  gnu/packages/patches/icecat-CVE-2015-0827-pt-1.patch,
  gnu/packages/patches/icecat-CVE-2015-0827-pt-2.patch,
  gnu/packages/patches/icecat-CVE-2015-0827-pt-3.patch,
  gnu/packages/patches/icecat-CVE-2015-0831-pt-1.patch,
  gnu/packages/patches/icecat-CVE-2015-0831-pt-2.patch,
  gnu/packages/patches/icecat-CVE-2015-0836-pt-01.patch,
  gnu/packages/patches/icecat-CVE-2015-0836-pt-02.patch,
  gnu/packages/patches/icecat-CVE-2015-0836-pt-03.patch,
  gnu/packages/patches/icecat-CVE-2015-0836-pt-04.patch,
  gnu/packages/patches/icecat-CVE-2015-0836-pt-05.patch,
  gnu/packages/patches/icecat-CVE-2015-0836-pt-06.patch,
  gnu/packages/patches/icecat-CVE-2015-0836-pt-07.patch,
  gnu/packages/patches/icecat-CVE-2015-0836-pt-08.patch,
  gnu/packages/patches/icecat-CVE-2015-0836-pt-09.patch,
  gnu/packages/patches/icecat-CVE-2015-0836-pt-10.patch,
  gnu/packages/patches/icecat-CVE-2015-0836-pt-11.patch: Remove files.
* gnu-system.am (dist_patch_DATA): Remove them.
* gnu/packages/gnuzilla.scm (icecat): Update to 31.5.0.  Remove patches.
  Add 'nspr', 'nss', and 'cairo' to inputs.  Add configure flags to use
  those system libraries.