Remove @brief commands from doxygen comments, too.

This is a follow-up to r331272.

We've been running doxygen with the autobrief option for a couple of
years now. This makes the \brief markers into our comments
redundant. Since they are a visual distraction and we don't want to
encourage more \brief markers in new code either, this patch removes
them all.

Patch produced by
  for i in $(git grep -l '\@brief'); do perl -pi -e 's/\@brief //g' $i & done

https://reviews.llvm.org/D46290

llvm-svn: 331275
diff --git a/llvm/lib/Support/Unix/Unix.h b/llvm/lib/Support/Unix/Unix.h
index 239a6d6..0c5d4de 100644
--- a/llvm/lib/Support/Unix/Unix.h
+++ b/llvm/lib/Support/Unix/Unix.h
@@ -56,7 +56,7 @@
 /// This function builds an error message into \p ErrMsg using the \p prefix
 /// string and the Unix error number given by \p errnum. If errnum is -1, the
 /// default then the value of errno is used.
-/// @brief Make an error message
+/// Make an error message
 ///
 /// If the error number can be converted to a string, it will be
 /// separated from prefix by ": ".