Remove \brief commands from doxygen comments.

Remove \brief commands from doxygen comments.

Summary:
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

[This is analogous to LLVM r331272 and CFE r331834]

Subscribers: srhines, nemanjai, javed.absar, kbarton, MaskRay, jkorous, arphaman, jfb, kadircet, jsji, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D66578

llvm-svn: 369643