mod+kvdb+channeldb: use btcwallet new DB interface

Depends on btcsuite/btcwallet#757.
Pulls in the updated version of btcwallet and walletdb that have the DB
interface enhanced by their own View() and Update() methods with the
reset callback/closure supported out of the box. That way the global
package-level View() and Update() functions now become pure redirects.

kvdb/go.sum

@@ -35,8 +35,8 @@ github.com/bgentry/speakeasy v0.1.0/go.mod h1:+zsyZBPWlz7T6j88CTgSN5bM796AkVf0kB
 github.com/bketelsen/crypt v0.0.3-0.20200106085610-5cbc8cc4026c/go.mod h1:MKsuJmJgSg28kpZDP6UIiPt0e0Oz0kqKNGyRaWEPv84=
 github.com/btcsuite/btclog v0.0.0-20170628155309-84c8d2346e9f h1:bAs4lUbRJpnnkd9VhRV3jjAVU7DJVjMaK+IsvSeZvFo=
 github.com/btcsuite/btclog v0.0.0-20170628155309-84c8d2346e9f/go.mod h1:TdznJufoqS23FtqVCzL0ZqgP5MqXbb4fg/WgDys70nA=
-github.com/btcsuite/btcwallet/walletdb v1.3.5-0.20210513043850-3a2f12e3a954 h1:CB6chiHPhZWmbCL7kFCADDf15V6I3EUNDgGC25jbptc=
-github.com/btcsuite/btcwallet/walletdb v1.3.5-0.20210513043850-3a2f12e3a954/go.mod h1:oJDxAEUHVtnmIIBaa22wSBPTVcs6hUp5NKWmI8xDwwU=
+github.com/btcsuite/btcwallet/walletdb v1.3.6-0.20210803004036-eebed51155ec h1:zcAU3Ij8SmqaE+ITtS76fua2Niq7DRNp46sJRhi8PiI=
+github.com/btcsuite/btcwallet/walletdb v1.3.6-0.20210803004036-eebed51155ec/go.mod h1:oJDxAEUHVtnmIIBaa22wSBPTVcs6hUp5NKWmI8xDwwU=
 github.com/census-instrumentation/opencensus-proto v0.2.1/go.mod h1:f6KPmirojxKA12rnyqOA5BBL4O983OfeGPqjHWSTneU=
 github.com/certifi/gocertifi v0.0.0-20191021191039-0944d244cd40/go.mod h1:sGbDF6GwGcLpkNXPUTkMRoywsNa/ol15pxFe6ERfguA=
 github.com/certifi/gocertifi v0.0.0-20200922220541-2c3bb06c6054 h1:uH66TXeswKn5PW5zdZ39xEwfS9an067BirqA+P4QaLI=