gnu: icecat: Add more fixes from upstream mozilla-esr52.
Includes fixes for CVE-2018-5104, CVE-2018-5097, CVE-2018-5099, and the
remaining 7 out of 21 changesets for CVE-2018-5089.
* gnu/packages/gnuzilla.scm (icecat)[source]: Add selected fixes from the
upstream mozilla-esr52 repository. Remove the local spectre mitigation patch
in favor of the (identical) changeset from upstream.
* gnu/packages/patches/icecat-bug-
1427870-spectre-mitigation.patch: Delete.
* gnu/local.mk (dist_patch_DATA): Remove it.