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/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index 189de14..cf35a2b 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -1635,7 +1635,7 @@
   Code = serialization::DECL_STATIC_ASSERT;
 }
 
-/// \brief Emit the DeclContext part of a declaration context decl.
+/// Emit the DeclContext part of a declaration context decl.
 void ASTDeclWriter::VisitDeclContext(DeclContext *DC) {
   Record.AddOffset(Writer.WriteDeclContextLexicalBlock(Context, DC));
   Record.AddOffset(Writer.WriteDeclContextVisibleBlock(Context, DC));