Revert "Add method to remove latest link"

This reverts commit 5b33d3a3.
Since the option to rm the bw file link has been removed from the
cli.

sbws/lib/v3bwfile.py

@@ -884,17 +884,6 @@ class V3BWFile(object):
         ys = [[getattr(l, k) for l in self.bw_lines] for k in attrs]
         return x, ys, attrs
 
-    def rm_link(self, output):
-        """"""
-        out_dir = os.path.dirname(output)
-        out_link = os.path.join(out_dir, 'latest.v3bw')
-        log.info('Removing %s link.', output)
-        with DirectoryLock(out_dir):
-            try:
-                os.unlink(out_link)
-            except FileNotFoundError:
-                pass
-
     def write(self, output, rm_link=False):
         if output == '/dev/stdout':
             log.info("Writing to stdout is not supported.")