fix: minimal-gas-prices and baseFeePerGas conflicts (#916)

* Problem: minimal-gas-prices and baseFeePerGas conflicts

Closes: #915

Solution:
- Don't check min-gas-price for evm tx if london hardfork and feemarket enabled.

comments and cleanup

changelog

* fix zero fee coins

Co-authored-by: Federico Kunze Küllmer <31522760+fedekunze@users.noreply.github.com>

x/evm/keeper/utils.go

@@ -66,6 +66,11 @@ func (k Keeper) DeductTxCostsFromUserBalance(
 		feeAmt = txData.Fee()
 	}
 
+	if feeAmt.Sign() == 0 {
+		// zero fee, no need to deduct
+		return sdk.NewCoins(), nil
+	}
+
 	fees := sdk.Coins{sdk.NewCoin(denom, sdk.NewIntFromBigInt(feeAmt))}
 
 	// deduct the full gas cost from the user balance