drop external gas recommendation

[sakulstra]

The aave app currently uses an external service for gas estimation.
In #33 I replaces gasnow with paraswap gas api, but while doing this I started wondering if we really need this.

Most interactions on the aave protocol don't need to happen fast.
Except for liquidations and swaps most transactions don't rely on timing - therefore I think i should be possible to completely drop the recommendation & instead go with the wallets getGasPrice/ rely on people speeding things up there.

Need to do some benchmarking on getGasPrice troughout supported wallets though.