This reverts commit 5fcfcea4.

Reason for revert:
1 Test Suite(s) failed. angle_unittests failed because of:
TestUtils.RunApp on Linux CFI
https://ci.chromium.org/p/chromium/builders/ci/Linux%20CFI


Original change's description:
> Add more test_utils functions.
> 
> Includes methods for creating temporary files, deleting files, and
> reading files into a string. Also renames GetPathSeparator to mention
> it's only used for environment variables. Includes a new virtual type
> angle::Process that will be used to implement cross-platform async
> Process launching for tests. Also includes a way to specify a custom
> crash handler callback.
> 
> Also adds a few unit tests for the new functionality. They are disabled
> on Android because the functions are not needed by the new test runner.
> 
> Bug: angleproject:3162
> Change-Id: I3e2c2e9837608884c98379fa0f78c9ffbe158d73
> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1821940
> Commit-Queue: Jamie Madill <jmadill@chromium.org>
> Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>

TBR=ynovikov@chromium.org,jonahr@google.com,jmadill@chromium.org

Change-Id: I1441bfbae31712f72b4aebeeea9cd711c3975a5d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: angleproject:3162
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1869254Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>