remove unused variables

[0xTimepunk]

We have a couple of unused variables detected while building, as well as function which can be restricted to view

Warning (2072): Unused local variable.
   --> lib/pigeon/src/hyperlane/HyperlaneHelper.sol:159:17:
    |
159 |                 bytes32 sender = log.topics[1];
    |                 ^^^^^^^^^^^^^^

Warning (2072): Unused local variable.
   --> lib/pigeon/src/hyperlane/HyperlaneHelper.sol:161:17:
    |
161 |                 bytes32 recipient = log.topics[3];
    |                 ^^^^^^^^^^^^^^^^^

Warning (2072): Unused local variable.
   --> lib/pigeon/src/layerzero/lib/LZPacket.sol:101:9:
    |
101 |         uint256 payloadSize = realSize - nonPayloadSize;

Warning (2018): Function state mutability can be restricted to view
   --> lib/pigeon/src/celer/CelerHelper.sol:269:5:
    |
269 |     function _estimateGas(
    |     ^ (Relevant source part starts here and spans across multiple lines).