Delete Payment Disclosures

This code will be "experimental" forever, only supports Sprout, and
is a piece of shit. Deleting with fire.

Sapling viewing keys are the replacement, which already exist.

qa/pull-tester/rpc-tests.sh

@@ -17,7 +17,6 @@ testScripts=(
     'dpow.py'
     'dpowconfs.py'
     'ac_private.py'
-    'paymentdisclosure.py'
     'prioritisetransaction.py'
     'wallet_treestate.py'
     'wallet_anchorfork.py'