client/providers: Update free evm providers.

[JoeGruffins]

Some of the hard coded providers we have are no longer working. We need to update them. We are able to see which are working using the tests in /dcrdex/client/asset/eth

I commented out the ones we know should fail and ran with go test --tags rpclive --run TestFreeServers. The results:

!!!! "https://eth.drpc.org" PASSED 
!!!! "https://eth-mainnet.nodereal.io/v1/1659dfb40aa24bbb8153a677b98064d7" PASSED 
XXXX "https://rpc.builder0x69.io" FAILED : connect error: failed to connect to even a single provider among: builder0x69.io 
XXXX "https://rpc.ankr.com/eth" FAILED : connect error: failed to connect to even a single provider among: ankr.com 
XXXX "https://ethereum.blockpi.network/v1/rpc/public" FAILED : connect error: failed to connect to even a single provider among: blockpi.network 
XXXX "https://rpc.flashbots.net" FAILED : "TransactionReceipt" error: not found 
XXXX "wss://eth.llamarpc.com" FAILED : "TransactionReceipt" error: context deadline exceeded

We may need to remove some and would be good to add some more. Same for polygon and testnet on both.

[JustinBeBoy]

I’ll look into it.