Changes --enable-verify-mar to be the default. Builds that want to disable mar verification will need to specify --disabled-verify-mar.
Removes --enable-verify-mar from Firefox's mozconfigs since it is no longer needed.
Re-enables app update browser chrome tests on ASAN that were disabled due to the ASAN mozconfigs not specifying --enable-verify-mar.
This also makes the same app update browser chrome tests on code coverage builds due to the code coverage mozconfigs not specifying --enable-verify-mar.
Differential Revision: https://phabricator.services.mozilla.com/D28288
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extra : moz-landing-system : lando
13aac1dde6