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/AST/CommentBriefParser.cpp b/clang/lib/AST/CommentBriefParser.cpp
index eecea8f..5ec7586 100644
--- a/clang/lib/AST/CommentBriefParser.cpp
+++ b/clang/lib/AST/CommentBriefParser.cpp
@@ -122,8 +122,8 @@
       if (Tok.is(tok::newline)) {
         ConsumeToken();
         // We found a paragraph end.  This ends the brief description if
-        // \\brief command or its equivalent was explicitly used.
-        // Stop scanning text because an explicit \\brief paragraph is the
+        // \command or its equivalent was explicitly used.
+        // Stop scanning text because an explicit \paragraph is the
         // preffered one.
         if (InBrief)
           break;