Change GMP precompile to rely only on amount transferred

[notlesh]

What does it do?

Internally, Wormhole does some "normalization" of asset amounts, relying on the wrapper ERC20's decimals() to modify the amount specified in the payload. The following fn is internally called by the bridge where decimals is taken from the ERC20:

    function deNormalizeAmount(
        uint256 amount,
        uint8 decimals
    ) internal pure returns (uint256) {
        if (decimals > 8) {
            amount *= 10 ** (decimals - 8);
        }
        return amount;
    }

The fix is quite simple: just detect the amount transferred (this was already done) and ignore the amount in the payload (previously we took the min() of the two).

While the fix is simple, I'd like a better understanding of the design behind the normalization technique, and I'd also like a way to catch this in tests.

[nbaztec]

I agree, a test would be great to have here, as an important change is in consideration.