Also removes the now unused ImportAddress and ImportScript from rpcdump.cpp
- No errors will be thrown when the script or key already exists in the wallet.
- If the key or script is already in the wallet, their labels will be updated.
This is a partial backport of Core PR16301 : https://github.com/bitcoin/bitcoin/pull/16301/commits/94bf156f391759420465b2ff8c44f5f150246c7f
Depends on D6413