Remove redundant ActivityLog key string constants

BUG=b:286851905
TEST=USE="coverage" FEATURES="test noclean" emerge-brya chromeos-base/gesture
LOW_COVERAGE_REASON=activity_replay is unit test code only

Change-Id: I68941312f4bd909c9221a3fa3c3c051adc099d08
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/gestures/+/4834762
Reviewed-by: Harry Cutts <hcutts@chromium.org>
Commit-Queue: Denis Brockus <dbrockus@chromium.org>
Code-Coverage: Zoss <zoss-cl-coverage@prod.google.com>
Tested-by: Denis Brockus <dbrockus@chromium.org>
4 files changed