libutils: remove the unused StopWatch lap functionality.

It's not tested, and it's not used. Also remove the fuzzer which is just
wasting CPU cycles.

This gets us to 100% function coverage, 100% line coverage, and N/A
branch coverage for StopWatch.

Test: treehugger
Change-Id: Ib5e08510ef1046a6f2af3f0b8a1c317a8bb39fd4