remove old is_terminating function

for InstructionData. Use generated `is_terminator()` for `Opcode`
instead. `is_terminator`, `can_trap` and `is_branch` functions are now
public.

fix syntax error

lib/cretonne/src/ir/instructions.rs

@@ -465,16 +465,6 @@ impl InstructionData {
             _ => CallInfo::NotACall,
         }
     }
-
-    /// Return true if an instruction is terminating, or false otherwise.
-    pub fn is_terminating<'a>(&'a self) -> bool {
-        match self {
-            &InstructionData::Jump { .. } => true,
-            &InstructionData::Return { .. } => true,
-            &InstructionData::Nullary { .. } => true,
-            _ => false,
-        }
-    }
 }
 
 /// Information about branch and jump instructions.