[thread.latch] Remove italics from non-definition of "latch".

Author: zygoloid

source/threads.tex

@@ -4919,9 +4919,8 @@
 
 \rSec2[thread.latch]{Latches}
 
-\indextext{latch|see{thread, latch}}%
 \pnum
-A \defnx{latch}{thread!latch} is a thread coordination mechanism
+A latch is a thread coordination mechanism
 that allows any number of threads to block
 until an expected number of threads arrive at the latch
 (via the \tcode{count_down} function).