Revert "Add optional flag to determine assertiveness level in aria announcement for flutter web" (#108262)

Fuchsia will soon remove all support for Component Framework version 1
components (recognized by component manifests ending in `.cmx`).
Notably, some of the `flutter` tool commands for Fuchsia devices--
notably, but not limited to, those related to CFv1--are outdated, and
either do not work today or soon won't work.

This PR removes the outdated components and commands, replacing some
with the newer version, or simply removing the non-working features,
in some cases.