pants: remove reporting links even if bad

fix for this error:

twitter/pants/goal/run_tracker.py", line 82, in __init__
OSError: [Errno 17] File exists

>> import os
>>> os.path.exists('.pants.d/runs/latest')
False
>>> os.path.lexists('.pants.d/runs/latest')
True
Merge pull request #57 from slackhappy/pants_rm_bad_links

pants: remove reporting links even if bad