Small fixes to screenshot->long screenshot transition

Hide the enterTransitionView so it doesn't conflict with the
"shared transition" view. Also turn off activity animations so
that the LongScreenshotActivity appears immediately instead of
fading in from the previous app.

Bug: 183197533
Test: manual
Change-Id: I6fba0012c72201f23c644148dde73a35627ee761
3 files changed