cmd/utils, node: remove unused solc references and improve RPC config (#14324)

Currently http cors and websocket origins are a comma separated string in the
config object. These are replaced with string arrays that are more expressive in
case of a config file.

internal/web3ext/web3ext.go

@@ -143,11 +143,6 @@ web3._extend({
 			call: 'admin_sleepBlocks',
 			params: 2
 		}),
-		new web3._extend.Method({
-			name: 'setSolc',
-			call: 'admin_setSolc',
-			params: 1
-		}),
 		new web3._extend.Method({
 			name: 'startRPC',
 			call: 'admin_startRPC',