Revert "Add fieldtrial_testing_config for Read Aloud Desktop."

This reverts commit b408089004512e0cd30fd81f5b209cfc2c5672ce.

Reason for revert: Need to be added back in because we need to extend
the end date on the experiment to iron out some crash issues

Original change's description:
> Add fieldtrial_testing_config for Read Aloud Desktop.
>
> Bug: 370826935
> Change-Id: Ie98b4306e9918829a798a880ab87277159741704
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5907930
> Reviewed-by: Kristi Saney <kristislee@google.com>
> Commit-Queue: Lauren Winston <lwinston@google.com>
> Cr-Commit-Position: refs/heads/main@{#1363973}

Bug: 370826935
Change-Id: Iac16b79b642d9c97dc088efa6253f15f307ed19e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5921368
Commit-Queue: Lauren Winston <lwinston@google.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1366325}