drop badger support (#869)

Makefile

cmd/geth/chaincmd.go

cmd/utils/flags.go

ethdb/AbstractKV.md

ethdb/abstractbench/abstract_bench_test.go

ethdb/database_test.go

ethdb/kv_abstract.go

ethdb/kv_abstract_test.go

ethdb/kv_badger.go

ethdb/memory_database.go

ethdb/object_db.go

go.mod

go.sum

node/config.go

node/node.go

node/service.go