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

Differential Revision: https://reviews.llvm.org/D46290

llvm-svn: 331272
diff --git a/llvm/lib/Target/ARC/ARCMCInstLower.h b/llvm/lib/Target/ARC/ARCMCInstLower.h
index 22e15cd..9a698f2 100644
--- a/llvm/lib/Target/ARC/ARCMCInstLower.h
+++ b/llvm/lib/Target/ARC/ARCMCInstLower.h
@@ -23,7 +23,7 @@
 class Mangler;
 class AsmPrinter;
 
-/// \brief This class is used to lower an MachineInstr into an MCInst.
+/// This class is used to lower an MachineInstr into an MCInst.
 class LLVM_LIBRARY_VISIBILITY ARCMCInstLower {
   using MachineOperandType = MachineOperand::MachineOperandType;
   MCContext *Ctx;