repair: remove unnecessary locking for bookmarks

The caller has already locked the repo.

mercurial/repair.py

@@ -216,9 +216,8 b' def strip(ui, repo, nodelist, backup=Tru'
         for m in updatebm:
             bm[m] = repo[newbmtarget].node()
 
-        with repo.lock():
-            with repo.transaction('repair') as tr:
-                bm.recordchange(tr)
+        with repo.transaction('repair') as tr:
+            bm.recordchange(tr)
 
         # remove undo files
         for undovfs, undofile in repo.undofiles():