Remove initial screenshot on interactive bugreport.

One of the changes in the 'interactive bugreport' bugreport workflow
introduced on N is that the initial screenshot was taken right away (by
Shell, not dumpstate).

Unfortunately, such initial screenshot is often delayed when the system
is overload. Also, if the user is not interested in a screenshot, it
would be adding more load on the system unnecessarily.

Given these issues, and the fact that the user can still easily take an
initial screenhsot by selecting the proper notification action, the
initial screenshot is being removed.

BUG: 28167977

Change-Id: I2cf6616ce3124102b62ec9a36dc5a0ce6455a909