gnu: ungoogled-chromium: Update to 81.0.4044.92-0.b484ad4 [security fixes].

gnu: ungoogled-chromium: Update to 81.0.4044.92-0.b484ad4 [security fixes].

This release fixes CVE-2020-6430, CVE-2020-6456, CVE-2020-6431, CVE-2020-6432,
CVE-2020-6433, CVE-2020-6434, CVE-2020-6435, CVE-2020-6436, CVE-2020-6437,
CVE-2020-6438, CVE-2020-6439, CVE-2020-6440, CVE-2020-6441, CVE-2020-6442,
CVE-2020-6443, CVE-2020-6444, CVE-2020-6445, CVE-2020-6446,  CVE-2020-6447,
and CVE-2020-6448.

* gnu/packages/chromium.scm (%preserved-third-party-files): Adjust for 81.
(%chromium-version): Set to 81.0.4044.92.
(%ungoogled-revision): Set to b484ad4c0bdb696c86d941798ae6b0e2bd0db35d.
(%debian-revision): Set to debian/81.0.4044.92-1.
(%chromium-origin, %ungoogled-origin, %debian-origin): Update hashes.
(ungoogled-chromium-source): Remove PYTHON-2 from the environment, use
PYTHON-WRAPPER instead.  Call "remove_bundled_libraries.py" using PYTHON-2
directly.
(ungoogled-chromium)[arguments]: Remove "is_cfi=false" from #:configure-flags.
Adjust CXXFLAGS to ignore unknown compiler warnings.
[inputs]: Change from ICU4C to ICU4C-66.1.