Nit: remove unused variable (#1153)

Unsure what the intention of this variable was, but doesn't do
anything now.

Signed-off-by: Eric Brown <eric_wade_brown@yahoo.com>

bandit/core/node_visitor.py

@@ -19,7 +19,6 @@ def __init__(
  ):
  self.debug = debug
  self.nosec_lines = nosec_lines
- self.seen = 0
  self.scores = {
  "SEVERITY": [0] * len(constants.RANKING),
  "CONFIDENCE": [0] * len(constants.RANKING),
@@ -209,7 +208,6 @@ def pre_visit(self, node):
  self.context["filename"] = self.fname
  self.context["file_data"] = self.fdata
 
- self.seen += 1
  LOG.debug(
  "entering: %s %s [%s]", hex(id(node)), type(node), self.depth
  )