gnu: icecat: Update to 38.3.0-gnu1.

* gnu/packages/patches/icecat-CVE-2015-4473-partial.patch,
  gnu/packages/patches/icecat-CVE-2015-4482.patch,
  gnu/packages/patches/icecat-CVE-2015-4488.patch,
  gnu/packages/patches/icecat-CVE-2015-4489.patch,
  gnu/packages/patches/icecat-CVE-2015-4491.patch,
  gnu/packages/patches/icecat-CVE-2015-4492.patch,
  gnu/packages/patches/icecat-CVE-2015-4495.patch,
  gnu/packages/patches/icecat-enable-acceleration-and-webgl.patch,
  gnu/packages/patches/icecat-libvpx-1.4.patch: Delete files.
* gnu/packages/patches/icecat-avoid-bundled-includes.patch: New file.
* gnu-system.am (dist_patch_DATA): Add new patch.  Remove the deleted ones.
* gnu/packages/gnuzilla.scm (icecat): Update to 38.3.0-gnu1.
  [source]: Add new patch.  Remove the deleted ones.
  [inputs]: Add libxcomposite.
  [arguments]: Add 'ensure-no-mtimes-pre-1980' phase.  Adapt
  'remove-h264parse-from-blacklist' and
  'arrange-to-link-libxul-with-libraries-it-might-dlopen' phases to the
  new version.