Update UI for Assistant optin flow

- Combined the get more screen and the ready screen.
- Updated strings and removed a button for voice match screen.

Bug: b/120666294
Test: Manual Test
Change-Id: Ieac56980f775752a32e9fda6d4646d1b2c6b7dcc
Reviewed-on: https://chromium-review.googlesource.com/c/1374747
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Yue Li <updowndota@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616902}
15 files changed