[Python] Remove unused variable last_line_content in viewcfg

Prior to this commit:

```
$ git grep last_line_content | wc -l
1
```

After this commit:

```
$ git grep last_line_content | wc -l
0
```

Author: practicalswift

utils/viewcfg

@@ -52,7 +52,6 @@ class Block(object):
     def __init__(self, name, preds):
         self.name = name
         self.content = None
-        self.last_line_content = None
         self.preds = []
         self.succs = None
         self.last_line = None