Remove GetAddressBalanceCmd.

Support for this extension request has been removed from btcwallet and
will not be returning.
IMPORT PATH MODIFICATION CHANGESET
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Please use this changeset as the first one on top of the conformal codebase.
Note that if there are new imports, they need to be changed as part of this
changeset. In general, use "git rebase" on github.com/conformal's version
and apply this changeset first.
Task #396 on Task Board:

Create a stub getdepositscript call for the websocket.

Can be called with method=getdepositscript. Parameters are currently ignored and the return value is a stub string.