Flow.kill: don't depend on reply status.

In principle, a flow is killable as long as the connection handler is still
checking the error status of the flow.

This is patch 2/4 of the reply-ectomy.

mitmproxy/flow.py

@@ -193,11 +193,7 @@ class Flow(stateobject.StateObject):
     @property
     def killable(self):
         """*Read-only:* `True` if this flow can be killed, `False` otherwise."""
-        return (
-            self.reply and
-            self.reply.state in {"start", "taken"} and
-            not (self.error and self.error.msg == Error.KILLED_MESSAGE)
-        )
+        return not (self.error and self.error.msg == Error.KILLED_MESSAGE)
 
     def kill(self):
         """

test/mitmproxy/test_http.py

@@ -7,7 +7,6 @@ import pytest
 
 from mitmproxy import flow
 from mitmproxy import flowfilter
-from mitmproxy.exceptions import ControlException
 from mitmproxy.http import Headers, Request, Response, HTTPFlow
 from mitmproxy.net.http.cookies import CookieAttrs
 from mitmproxy.test.tflow import tflow
@@ -704,10 +703,11 @@ class TestHTTPFlow:
 
     def test_kill(self):
         f = tflow()
-        with pytest.raises(ControlException):
-            f.intercept()
-            f.resume()
-            f.kill()
+        f.intercept()
+        f.resume()
+        assert f.killable
+        f.kill()
+        assert not f.killable
 
         f = tflow()
         f.intercept()