[split-node] Revert splitting setupDB

[jellonek]

Turns out that splitting databases require more work and was improperly tested.

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
12407	1	12406	5

View the top 1 failed tests by shortest run time

github.com/spacemeshos/go-spacemesh/p2p/pubsub TestGossip

Stack Traces | 10s run time

=== RUN   TestGossip
    pubsub_test.go:43: 
        	Error Trace:	.../p2p/pubsub/pubsub_test.go:43
        	Error:      	Condition never satisfied
        	Test:       	TestGossip
--- FAIL: TestGossip (10.00s)

To view more test analytics, go to the Test Analytics Dashboard
📢 Thoughts on this report? Let us know!