Revert "[Telemetry] add features chromeos_system_extension"

This reverts commit 4671685ce96a840c51e5ccf11b2a8dbfc6302cdf.

Reason for revert: 
TelemetryExtensionBrowserTest.CanReceiveMessageExternal fails on linux-chromeos-rel

BUG=1248625

Original change's description:
> [Telemetry] add features chromeos_system_extension
>
> Enable chromeos_system_extension type of extensions to define the
> following manifest key: externally_connectable.
>
> Also allow the extension type to access the api: chrome.runtime.*.
>
> Bug: b:188897824, 1229585
> Test: added browser_test in telemetry_extension_capabilities_browser_test.cc
> Test: browser_tests --gtest_filter="*CanReceiveMessageExternal*" Green
>
> Change-Id: Ie2127565bb6d7084b5d5ff1ff27818381380ef21
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3114300
> Commit-Queue: Mahmoud Gawad <mgawad@google.com>
> Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
> Reviewed-by: Oleh Lamzin <lamzin@google.com>
> Cr-Commit-Position: refs/heads/main@{#920394}

Bug: b:188897824, 1229585
Change-Id: I9a06d675478d20b4b063dbd9a55d46d347712214
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3155722
Auto-Submit: Ahmed Fakhry <afakhry@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Owners-Override: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/main@{#920429}