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/LayoutOverrideSource.cpp b/clang/lib/Frontend/LayoutOverrideSource.cpp
index 06e9a7d..93e07eb 100644
--- a/clang/lib/Frontend/LayoutOverrideSource.cpp
+++ b/clang/lib/Frontend/LayoutOverrideSource.cpp
@@ -15,7 +15,7 @@
 
 using namespace clang;
 
-/// \brief Parse a simple identifier.
+/// Parse a simple identifier.
 static std::string parseName(StringRef S) {
   if (S.empty() || !isIdentifierHead(S[0]))
     return "";