Bumps lnd to v0.21.0-beta, lndclient to v0.21.0-1, and
taproot-assets to v0.8.0 across the root, litrpc, and perms
modules. taprpc uses the proper v1.1.0 tag.
lnd removed the deprecated SendPaymentSync, SendToRouteSync,
SendPayment (streaming), and SendToRoute (streaming) RPCs. The
account interceptor checkers and their tests for these RPCs are
removed since no client can call them anymore. The V2 checkers
already handle account tracking for payments.
The itest harness is updated for lnd v0.21's miner API changes
(SendOutputs -> SendOutput, Miner.Client.Generate -> GenerateBlocks,
waitForNTxsInMempool replaced by Miner.AssertNumTxsInMempool) and
TimeLockDelta bumped from 20 to 40 since lnd v0.21 raised
MinCLTVDelta from 18 to 24.
