chore: remove deprecated shift word

contracts/implementations/ChildGauge.vy

@@ -277,14 +277,14 @@ def _checkpoint_rewards(_user: address, _total_supply: uint256, _claim: bool, _r
  new_claimable = user_balance * (integral - integral_for) / 10**18
 
  claim_data: uint256 = self.claim_data[_user][token]
- total_claimable: uint256 = shift(claim_data, -128) + new_claimable
+ total_claimable: uint256 = (claim_data >> 128) + new_claimable
  if total_claimable > 0:
  total_claimed: uint256 = claim_data % 2**128
  if _claim:
  assert ERC20(token).transfer(receiver, total_claimable, default_return_value=True)
  self.claim_data[_user][token] = total_claimed + total_claimable
  elif new_claimable > 0:
- self.claim_data[_user][token] = total_claimed + shift(total_claimable, 128)
+ self.claim_data[_user][token] = total_claimed + (total_claimable << 128)
 
 
 @internal
@@ -771,7 +771,7 @@ def claimable_reward(_user: address, _reward_token: address) -> uint256:
  integral_for: uint256 = self.reward_integral_for[_reward_token][_user]
  new_claimable: uint256 = self.balanceOf[_user] * (integral - integral_for) / 10**18
 
- return shift(self.claim_data[_user][_reward_token], -128) + new_claimable
+ return (self.claim_data[_user][_reward_token] >> 128) + new_claimable
 
 
 @external