Remove useless test to fix data race

[gerardsn]

fixes race condition

==================
WARNING: DATA RACE
Write at 0x00c000114ca0 by goroutine 797:
  github.com/daangn/minimemcached.(*server).close()
      /home/circleci/go/pkg/mod/github.com/daangn/[email protected]/server.go:27 +0xc4
  github.com/daangn/minimemcached.(*MiniMemcached).Close()
      /home/circleci/go/pkg/mod/github.com/daangn/[email protected]/minimemcached.go:90 +0x77
  github.com/nuts-foundation/nuts-node/storage.memcachedTestServer.func1()
      /home/circleci/project/storage/session_memcached_test.go:180 +0x2e
  testing.(*common).Cleanup.func1()
      /usr/local/go/src/testing/testing.go:1176 +0x179
  testing.(*common).runCleanup()
      /usr/local/go/src/testing/testing.go:1354 +0x261
  testing.tRunner.func2()
      /usr/local/go/src/testing/testing.go:1684 +0x50
  runtime.deferreturn()
      /usr/local/go/src/runtime/panic.go:605 +0x5d
  testing.(*T).Run.gowrap1()
      /usr/local/go/src/testing/testing.go:1743 +0x44

Previous read at 0x00c000114ca0 by goroutine 799:
  github.com/daangn/minimemcached.(*MiniMemcached).serve()
      /home/circleci/go/pkg/mod/github.com/daangn/[email protected]/minimemcached.go:125 +0x4f
  github.com/daangn/minimemcached.(*MiniMemcached).newServer.func1()
      /home/circleci/go/pkg/mod/github.com/daangn/[email protected]/minimemcached.go:119 +0x2e

Goroutine 797 (running) created at:
  testing.(*T).Run()
      /usr/local/go/src/testing/testing.go:1743 +0x825
  testing.runTests.func1()
      /usr/local/go/src/testing/testing.go:2168 +0x85
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:1690 +0x226
  testing.runTests()
      /usr/local/go/src/testing/testing.go:2166 +0x8be
  testing.(*M).Run()
      /usr/local/go/src/testing/testing.go:2034 +0xf17
  main.main()
      _testmain.go:137 +0x164

Goroutine 799 (finished) created at:
  github.com/daangn/minimemcached.(*MiniMemcached).newServer()
      /home/circleci/go/pkg/mod/github.com/daangn/[email protected]/minimemcached.go:118 +0x8d
  github.com/daangn/minimemcached.(*MiniMemcached).start()
      /home/circleci/go/pkg/mod/github.com/daangn/[email protected]/minimemcached.go:113 +0xe4
  github.com/daangn/minimemcached.Run()
      /home/circleci/go/pkg/mod/github.com/daangn/[email protected]/minimemcached.go:83 +0x6a
  github.com/nuts-foundation/nuts-node/storage.memcachedTestServer()
      /home/circleci/project/storage/session_memcached_test.go:175 +0xc4
  github.com/nuts-foundation/nuts-node/storage.memcachedTestDatabase()
      /home/circleci/project/storage/session_memcached_test.go:157 +0x3b
  github.com/nuts-foundation/nuts-node/storage.TestNewMemcachedSessionDatabase()
      /home/circleci/project/storage/session_memcached_test.go:34 +0x26
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:1690 +0x226
  testing.(*T).Run.gowrap1()
      /usr/local/go/src/testing/testing.go:1743 +0x44
==================

[woutslakhorst]

ack, based on the idea that the other tests use the DB resulting in a "wait for startup" kind of behaviour