Fix visibility of dismiss button in ToC tutorial

The @dimen/wrap_content hack doesn't work on all devices.
Using fixed value instead.

Ideally, the image should be exactly square.
In a later patch the image could be adjusted from
130x128 to 128x128.

Bug: 72595
Change-Id: I02e87782988205ab6e2f8d2ccd8bc0d54858503b