Rename AutofillClient::StartSigninFlow() to ExecuteCommand()
Rename AutofillClient::StartSigninFlow() to ExecuteCommand()

https://crrev.com/04fc429cf5d4c16316402d43c5435c36d09c480f

brave/muon,brave/muon,brave/muon,brave/electron,brave/electron,brave/muon,brave/muon,brave/muon,brave/electron,brave/electron,brave/electron,brave/electron