Remove @brief commands from doxygen comments, too.

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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@331275 91177308-0d34-0410-b5e6-96231b3b80d8