cleanup: use stat_result[stat.ST_MTIME] instead of stat_result.st_mtime The latter is floating point by default, and we've been doing os.stat_float_times(False). Unfortunately, os.stat_float_times was removed between Python 3.7.0a1 and 3.7.0b2, so we have to stop using it. Differential Revision: https://phab.mercurial-scm.org/D2696