Bump dcrwallet dependency to v4.2.0 (release v2.0.5) #668

Job	Run time
Build (1.21)	2m 47s
Build (1.22)	2m 36s
Test (1.21, unit-race)	17m 14s
Test (1.21, itest-parallel-run)	28m 54s
Test (1.21, itest-parallel-run walletimpl=embeddedwallet_dcrw)	28m 22s
Test (1.21, itest-parallel-run walletimpl=embeddedwallet_dcrw backend=spv)	27m 55s
Test (1.21, itest-parallel-run walletimpl=remotewallet)	31m 13s
Test (1.21, itest-parallel-run walletimpl=remotewallet backend=spv)	30m 39s
	2h 49m 40s

Provide feedback