[cef][wam] Make the recipe work with official chromium release tarballs

This change drops the chromium mirror repository that was being used for
milestone 108 in favor of using the official release tarballs from
https://commondatastorage.googleapis.com/chromium-browser-official in an effort
to make it easier to upgrade the current chromium milestones (also to improve
download and build times).

Also, the current milestone is being upgraded from 108 to 118.

Bug-AGL: SPEC-3872

Signed-off-by: Roger Zanoni <rzanoni@igalia.com>
Change-Id: Iba4a94ef762d278864114c02bb9e36a308ff5a7a
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl-demo/+/29417
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
ci-image-build: Jenkins Job builder account
Tested-by: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account