tests: use silenttestrunner in test-simplemerge.py The time monkeypatching doesn't appear to work reliably in Python 3, possibly due to unittest using a different time function. This makes the test intermittent due to the execution time not always being `0.00s`. We have our own wrapper around unittest for more deterministic test output. So let's use it. As a bonus, all test output disappeared, so we can remove the .out file! Differential Revision: https://phab.mercurial-scm.org/D6921