Don't plot usage data beyond current date.

- the new data usage api returns buckets for future date with 0 usage.
When we plot the data usage chart, need to check the bucket date to make
sure we only plot points up to the current date.

Change-Id: I50e161ca9cdbb30c8fda8f6cdd24c993b546ad0d
Fixes: 120490567
Test: make RunSettingsRoboTests