Revert "[Read aloud] Remove legacy code that is no longer needed"

This reverts commit fc01515e112ea2301c2c6e571bbbcf7d2691cc40.

Reason for revert: Previously enabled languages for now unavailable voices will now be re-enabled (e.g. pt-pt previously enabled will cause pt-br to be re-enabled when pt-pt is no longer available). Since this may break ChromeOS, we should rollback and fix and the Windows issue separately

Original change's description:
> [Read aloud] Remove legacy code that is no longer needed
>
> The issue this was fixing is no longer relevant, and it's causing
> problems now.
>
> Bug: 379174194
>
> Change-Id: I214d0626916f687bb7e0063072141b446f185e4c
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6026691
> Auto-Submit: Kristi Saney <kristislee@google.com>
> Reviewed-by: Lauren Winston <lwinston@google.com>
> Commit-Queue: Lauren Winston <lwinston@google.com>
> Cr-Commit-Position: refs/heads/main@{#1383854}

Bug: 379174194
Change-Id: I6b7caa830dbd9ccbf7cf0e4a52b52105b76040d1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6036266
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Lauren Winston <lwinston@google.com>
Reviewed-by: Kristi Saney <kristislee@google.com>
Cr-Commit-Position: refs/heads/main@{#1385247}