Remove \brief commands from doxygen comments.

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

lib/TBDGen/tapi/InterfaceFile.cpp

@@ -8,7 +8,7 @@
 //===----------------------------------------------------------------------===//
 ///
 /// \file
-/// \brief Implements the Interface File
+/// Implements the Interface File
 ///
 //===----------------------------------------------------------------------===//