Remove command line/field trial support for disabling Isolate Extensions.
The Isolate Extensions project/feature shipped on by default in M56.
This CL removes the support for disabling Isolate Extensions, which
includes field trial config, supporting code, command line parameter,
and tests that are no longer relevant.
BUG=545200
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation
Review-Url: https://codereview.chromium.org/2850793005
Cr-Commit-Position: refs/heads/master@{#468898}
28 files changed
