Revert "PrepareProposal-VoteExtension integration (#6915)" (#7769)

This reverts commit 39ffa80ae7.

Nightly end-to-end tests are currently failing; revert temporarily so we can
debug.

types/block.go

@@ -518,8 +518,7 @@ func (h *Header) StringIndented(indent string) string {
 		indent, h.LastResultsHash,
 		indent, h.EvidenceHash,
 		indent, h.ProposerAddress,
-		indent, h.Hash(),
-	)
+		indent, h.Hash())
 }
 
 // ToProto converts Header to protobuf