Revert "Let lld emit colored diagnostics when invoked from ninja."

This reverts commit 00db3ddc4c4f9ebd4d95ad44ea4ef74415c66394.

Reason for revert: Breaks Linux CFI build here: https://ci.chromium.org/buildbot/chromium.memory/Linux%20CFI/8024

Original change's description:
> Let lld emit colored diagnostics when invoked from ninja.
> 
> Bug: 841221
> Change-Id: I72d13c78a2c623865a4f29542d25f6b3488b350b
> Reviewed-on: https://chromium-review.googlesource.com/1067460
> Reviewed-by: Reid Kleckner <rnk@chromium.org>
> Commit-Queue: Nico Weber <thakis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#560343}

TBR=thakis@chromium.org,rnk@chromium.org

Change-Id: I3811083daa622dca605ca32be5cc4c7098b60b4a
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 841221
Reviewed-on: https://chromium-review.googlesource.com/1067949
Reviewed-by: Tommy Li <tommycli@chromium.org>
Commit-Queue: Tommy Li <tommycli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#560345}

• build/config/compiler/BUILD.gn[diff]