Hide link icon if text is empty

A link icon is shown without explaining text or a link.
The reason is that the getFooterLearnMore text is empty.
We solve this by hiding the link icon if footer text is
empty on first fingerprint enrollment screen.

Bug: 266530752
Test: Manual
Flag: EXEMPT bugfix
(cherry picked from https://partner-android-review.googlesource.com/q/commit:75334e58aee193379788530e702ec60ab8f8127f)
Merged-In: I35f421e3cb4cdeee5a420e2ddf0fae2520cbd4ba
Change-Id: I35f421e3cb4cdeee5a420e2ddf0fae2520cbd4ba