[Wallet] Watch-only fixes

- prevent importaddress if the wallet already contains the private key
- remove from watchonly, if you import the private key. (note that you need to restart to get the correct eye-icons in this scenario as updating dynamically would require some more fiddling with signals etc.)
- do not add locked watchonly to coincontrol. (we shouldnt allow locking watchonly in the first place, but thats for another pull)
- remove LOCKs from rpcdump.cpp for consistence
- add filter to GetCredit, fixes #4870 (also revert the 1 line from #4825 where we changed the filter to bool)

Coding style (space after if).