[tricium cpplint] Disable build/header_guard and runtime/explicit in src

The build/header_guard isn't working for the cpplint analyzer
right now, which is creating a lot of noise.

Disabling runtime/explicit for now because of discussion
in https://chromium-review.googlesource.com/c/chromium/src/+/1415258.

TBR=maruel
TBR_REASON=this is a small config change that should be committed
quickly because it fixes an issue that is creating noise for many people.

Bug: 924326
Change-Id: Ie904b445cf0babc9f2a61ae5f62734f0b5402d0d
Reviewed-on: https://chromium-review.googlesource.com/c/1427932Reviewed-by: Quinten Yearsley <qyearsley@chromium.org>
Commit-Queue: Quinten Yearsley <qyearsley@chromium.org>
Cr-Commit-Position: refs/heads/master@{#624984}

infra/config/global/tricium-prod.cfg

@@ -11,7 +11,7 @@ selections {
   platform: UBUNTU
   configs {
     name: "filter"
-    value: "-,+readability/todo,+readability/check,+readability/casting,+readability/fn_size,+runtime/explicit,+build/include_what_you_use,+build/header_guard,+build/include_order"
+    value: "-,+readability/todo,+readability/check,+readability/casting,+readability/fn_size,+build/include_what_you_use,+build/include_order"
   }
 }