labels are associated with addresses (rather than addresses being
associated with labels, as was the case with accounts). The
getlabeladdress does not make sense in this model, so remove it.
getaccountaddress is still supported for one release as the accounts
API is deprecated.
Backport of Core PR13060
https://github.com/bitcoin/bitcoin/pull/13060/commits/81608178cff793ee205a4f70481c76d34c5448a4
Depends on D4518