Clean up ConditionTracker variables for tracking unsliced condition

Variables mNonSlicedConditionState and mUnSlicedPart both track the
unsliced condition in ConditionTrackers. However, they are used
inconsistently. These variables can be replaced with one variable and
duplicate logic can be cleaned up.

Bug: b/157079077
Test: m statsd_test && adb sync data && adb shell data/nativetest/statsd_test/statsd_test
Change-Id: I00b577e09a1fd703624eb61eabf2e1c6fee26731