patman: Drop unused signoff member

This is not used. Drop it.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/patman/func_test.py

@@ -16,6 +16,7 @@ import unittest
 from patman import control
 from patman import gitutil
 from patman import patchstream
+from patman.patchstream import PatchStream
 from patman import settings
 from patman import terminal
 from patman import tools

tools/patman/patchstream.py

@@ -79,7 +79,6 @@ class PatchStream:
         self.change_lines = []           # Lines of the current change
         self.blank_count = 0             # Number of blank lines stored up
         self.state = STATE_MSG_HEADER    # What state are we in?
-        self.signoff = []                # Contents of signoff line
         self.commit = None               # Current commit
 
     def _add_warn(self, warn):