fix imports in graph.py

Although graph.py never used DisAsm, it was still trying to import the
deprecated class. Removed.

original-commit-id: 74a4d6588458a05d2e833f12ea2c80df10b0865d

graph.py

@@ -2,9 +2,12 @@
 
 import networkx as nx
 
-from romstr import RomStr, DisAsm, \
-    relative_jumps, call_commands, \
-    relative_unconditional_jumps
+from romstr import (
+    RomStr,
+    relative_jumps,
+    call_commands,
+    relative_unconditional_jumps,
+)
 
 class RomGraph(nx.DiGraph):
     """ Graphs various functions pointing to each other.