Remove FeedbackLog instance variables.

For a while, the ResearchLogger supported comprehensive recording of the
last few words in case the user wished to upload this data to give
developers feedback.  However, this mechanism was not implemented well
(keeping a separate copy of the data), did not make the collected data
clear to the user, and was not working properly in the latest build (NPEs).
The mechanism in fact was deprecated in favor of the "userRecording"
mechanism in which the user explicitly turned on comprehensive recording,
demonstrated the issue they were experiencing, and then turned it off.

This change removes the vestiges of the FeedbackLogging mechanism.
A feedback log is still used to hold the user's message, but it is created
in a local variable as-needed, and not persisted in ResearchLogger.

Change-Id: I6a09d0ed36e1eddb6e57895e7428d22107f75f49