Revert change to FBSession close that would have no-op if state is al…

…ready closed.

Summary: Revert change to FBSession close that would have no-op if state is already closed.

Test Plan:
Quickly tested scrumptious on 5.1 and 6.0 login/logout/post.

Revert Plan:

Reviewers: jacl

Reviewed By: jacl

Differential Revision: https://phabricator.fb.com/D588757

Task ID: 1764202

src/FBSession.m

@@ -404,9 +404,6 @@ - (void)close {
     NSAssert(self.affinitizedThread == [NSThread currentThread], @"FBSession: should only be used from a single thread");
 
     FBSessionState state;
-    if (self.state = FBSessionStateClosed) {
-        return;
-    }
     if (self.state == FBSessionStateCreatedOpening) {
         state = FBSessionStateClosedLoginFailed;
     } else {