Fix buttons and icons for fingerprint enroll intro

Updates the labels of buttons and the colors of icons shown on the
fingerprint enroll intro screen to be consistent with the face enroll
intro screen and match the latest mocks.

Note that this commit removes some unused strings but does not add any
new ones requiring l10n.

Test: Manually tested face enroll from Setup Wizard and Settings

Fixes: 192381823
Change-Id: Id991d4f29d6de82acd538f1853bc8a5e50cd2637