Revert r28050 due to crashes with --optimization-counter-threshold=5.

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
===================================================================
--- runtime/vm/intermediate_language.h	(revision 28051)
+++ runtime/vm/intermediate_language.h	(working copy)
@@ -1179,8 +1179,6 @@
     return parallel_move_;
   }
 
-  bool IsEmptyBlock();
-
   // Discover basic-block structure by performing a recursive depth first
   // traversal of the instruction graph reachable from this instruction.  As
   // a side effect, the block entry instructions in the graph are assigned
@@ -1254,10 +1252,6 @@
 
   void set_block_id(intptr_t block_id) { block_id_ = block_id; }
 
-  // For all instruction in this block: Remove all inputs (including in the
-  // environment) from their definition's use lists for all instructions.
-  void ClearAllInstructions();
-
  protected:
   BlockEntryInstr(intptr_t block_id, intptr_t try_index)
       : block_id_(block_id),