Remove unused variables in instructions

mythril/laser/ethereum/instructions.py

@@ -503,7 +503,6 @@ class Instruction:
         global keccak_function_manager
 
         state = global_state.mstate
-        environment = global_state.environment
         op0, op1 = state.stack.pop(), state.stack.pop()
 
         try:
@@ -711,7 +710,6 @@ class Instruction:
             _bytes = util.concrete_int_to_bytes(value)
 
             i = 0
-
             for b in _bytes:
                 state.memory[mstart + i] = _bytes[i]
                 i += 1
@@ -956,7 +954,7 @@ class Instruction:
         state = global_state.mstate
         dpth = int(self.op_code[3:])
         state.stack.pop(), state.stack.pop()
-        [state.stack.pop() for x in range(dpth)]
+        [state.stack.pop() for _ in range(dpth)]
         # Not supported
         return [global_state]