Expand icon should not appear on Rewards webview on Android

[zenparsing]

Description

On Android, when the Rewards page is opened as a webview, the expand button should not be displayed.

Rationale: The expand button takes the user to the "full Rewards page" in a new tab. On Android phones, the UI for the tab and the bubble (webview) are the same, so redirecting to a tab is not useful.

Steps to reproduce

1. Open the Android Rewards webview

Actual result

The expand button is displayed.

Expected result

The expand button should not be displayed.

Reproduces how often

Easily reproduced

Brave version

1.77.x

Device

any

Channel information

• release (stable)
• beta
• nightly

Reproducibility

• with Brave Shields disabled
• with Brave Rewards disabled
• in the latest version of Chrome

Miscellaneous information

No response