gnu: icecat: Update to 78.3.0-guix0-preview1 [security-fixes].

gnu: icecat: Update to 78.3.0-guix0-preview1 [security-fixes].

Includes fixes for CVE-2020-15673, CVE-2020-15676, CVE-2020-15677, and
CVE-2020-15678.

* gnu/packages/gnuzilla.scm (mozilla-compare-locales): Update to
RELEASE_8_0_0.
(all-mozilla-locales): Update to newer versions.
(mozilla-patch): Remove vestigial procedure.
(%icecat-version, %icecat-build-id): Update to 78.3.0-guix0-preview1.
(icecat-source): Update 'upstream-icecat-base-version', 'gnuzilla-commit', and
hashes.  Reverse order of makeicecat-patch and gnuzilla-fixes-patch.
(icecat)[inputs]: Remove libogg, libvorbis, libvpx, icu4c, sqlite,
startup-notification, and zlib.  Add several "UNBUNDLE-ME!" comments.
[native-inputs]: Update 'rust' and 'cargo' dependencies to version 1.41.
Update 'rust-cbindgen' dependency to version 0.14.  Update 'node' dependency
to 10.22.
[arguments]<configure-flags>: Change --enable-default-toolkit value to
"cairo-gtk3-wayland".  Change --with-unsigned-addon-scopes value to
"app,system".  Add "--allow-addon-sideload".  Remove
"--enable-startup-notification" and "--disable-gconf".  Comment out
"--with-system-zlib", "--with-system-bz2", and "--with-system-icu".
<phases>: In the 'remove-bundled-libaries' phase, remove "modules/zlib" from
the list of directories to delete.  Update the 'patch-cargo-checksums' phase
to update more modules.
(mozilla-68-compare-locales, all-mozilla-68-locales, %icecat-68-version)
(icecat-68-source): New variables preserving the previous icecat 68 source.
(icedove)[source]: Use 'icecat-68-source'.
* gnu/packages/patches/icecat-makeicecat.patch: Adapt to IceCat 78.
* gnu/packages/patches/icecat-68-makeicecat.patch: New file containing
the previous 'icecat-makeicecat.patch'.
* gnu/local.mk: Add 'icecat-68-makeicecat.patch'.