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/Basic/DiagnosticIDs.cpp b/clang/lib/Basic/DiagnosticIDs.cpp
index b25057f..697de68 100644
--- a/clang/lib/Basic/DiagnosticIDs.cpp
+++ b/clang/lib/Basic/DiagnosticIDs.cpp
@@ -340,7 +340,7 @@
          getBuiltinDiagClass(DiagID) != CLASS_ERROR;
 }
 
-/// \brief Determine whether the given built-in diagnostic ID is a
+/// Determine whether the given built-in diagnostic ID is a
 /// Note.
 bool DiagnosticIDs::isBuiltinNote(unsigned DiagID) {
   return DiagID < diag::DIAG_UPPER_LIMIT &&
@@ -412,7 +412,7 @@
   return toLevel(getDiagnosticSeverity(DiagID, Loc, Diag));
 }
 
-/// \brief Based on the way the client configured the Diagnostic
+/// Based on the way the client configured the Diagnostic
 /// object, classify the specified diagnostic ID into a Level, consumable by
 /// the DiagnosticClient.
 ///