fbamend: remove troublesome tr.release()

Summary:
`tr` could be None and `tr.release()` there is causing issues.

The next line actually checks `tr` and call `tr.release()` if `tr` is not None.

Test Plan: arc unit

Reviewers: #mercurial, wez

Reviewed By: wez

Subscribers: medson, mjpieters

Differential Revision: https://phabricator.intern.facebook.com/D5314538

Signature: t1:5314538:1498255892:084e1f5f1521ff7794be43b24510d2b54bf2148e

hgext3rd/fbamend/split.py

@@ -118,7 +118,6 @@ def split(ui, repo, *revs, **opts):
                 common.restackonce(ui, repo, top, inhibithack=True)
         tr.close()
     finally:
-        tr.release()
         lockmod.release(tr, lock, wlock)
 
     # clean up possibly incorrect rebasestate