[futures.shared_future] Remove duplicated word "shared"

jwilk · jwilk · commit f35f6e7c5e2a · 2016-02-26T12:00:05.000+01:00
diff --git a/source/threads.tex b/source/threads.tex
@@ -4368,7 +4368,7 @@
 
 \pnum
 \enternote Member functions of \tcode{shared_future} do not synchronize with themselves,
-but they synchronize with the shared shared state. \exitnote
+but they synchronize with the shared state. \exitnote
 
 \pnum
 The effect of calling any member function other than the destructor, the move-assignment
