Remove \brief commands from doxygen comments.

This is similar to the LLVM change https://reviews.llvm.org/D46290.

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

Differential Revision: https://reviews.llvm.org/D46320

llvm-svn: 331834
diff --git a/clang/lib/Frontend/Rewrite/FixItRewriter.cpp b/clang/lib/Frontend/Rewrite/FixItRewriter.cpp
index 17a35c3..64785e3 100644
--- a/clang/lib/Frontend/Rewrite/FixItRewriter.cpp
+++ b/clang/lib/Frontend/Rewrite/FixItRewriter.cpp
@@ -194,7 +194,7 @@
   Diag(Info.getLocation(), diag::note_fixit_applied);
 }
 
-/// \brief Emit a diagnostic via the adapted diagnostic client.
+/// Emit a diagnostic via the adapted diagnostic client.
 void FixItRewriter::Diag(SourceLocation Loc, unsigned DiagID) {
   // When producing this diagnostic, we temporarily bypass ourselves,
   // clear out any current diagnostic, and let the downstream client