Revert "infra: Add and use mixins for Goma RBE server settings"

This reverts commit 58e8d8c6b5211092e7ea0effb1f176e0404aca19.

Reason for revert: Cannot combine mixins

Original change's description:
> infra: Add and use mixins for Goma RBE server settings
> 
> R=​tikuta@chromium.org, ukai@chromium.org, yyanagisawa@chromium.org
> 
> Bug: 945701
> Change-Id: I98b2a8a2d644eccde84224171bbe7e9885041046
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1539416
> Commit-Queue: Simon Que <sque@chromium.org>
> Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#644219}

TBR=sque@chromium.org,ukai@chromium.org,yyanagisawa@chromium.org,tikuta@chromium.org

Change-Id: Ife0174d62bec2bf99d75647b864fd6c7992fa30e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 945701
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1539490
Reviewed-by: Simon Que <sque@chromium.org>
Commit-Queue: Simon Que <sque@chromium.org>
Cr-Commit-Position: refs/heads/master@{#644690}
1 file changed