Fix documentation string for chrome.enterprise.kioskInput API

Remove old reference to ChromeApps support. This API only support
extensions.

Change-Id: I1e578e9ca914c5cd1daaa95b7720b253e6b81bb8
Bug: b:330835940
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5412954


Reviewed-by: Devlin Cronin <rdevlin.cronin@chromium.org>
Commit-Queue: Emmanuel Arias Soto <eariassoto@google.com>
Cr-Commit-Position: refs/heads/main@{#1281714}