Remove old code to count number of resource owners backed up (#2414)

## Description

Remove unused code that counted the number of resource owners that participated in the backup. This is no longer required as we've restricted each backup to act on a single resource owner

## Does this PR need a docs update or release note?

- [ ] ✅ Yes, it's included
- [ ] 🕐 Yes, but in a later PR
- [x] ⛔ No 

## Type of change

- [ ] 🌻 Feature
- [ ] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Test
- [ ] 💻 CI/Deployment
- [x] 🧹 Tech Debt/Cleanup

## Test Plan

- [ ] 💪 Manual
- [x] ⚡ Unit test
- [ ] 💚 E2E

src/internal/data/data_collection.go

@@ -86,38 +86,3 @@ type StreamSize interface {
 type StreamModTime interface {
 	ModTime() time.Time
 }
-
-// ------------------------------------------------------------------------------------------------
-// functionality
-// ------------------------------------------------------------------------------------------------
-
-// ResourceOwnerSet extracts the set of unique resource owners from the
-// slice of Collections.
-func ResourceOwnerSet(cs []Collection) []string {
-	rs := map[string]struct{}{}
-
-	for _, c := range cs {
-		fp := c.FullPath()
-		if fp == nil {
-			// Deleted collections have their full path set to nil but the previous
-			// path will be populated.
-			fp = c.PreviousPath()
-		}
-
-		if fp == nil {
-			// This should not happen, but keep us from hitting a nil pointer
-			// exception if it does somehow occur. Statistics will be off though.
-			continue
-		}
-
-		rs[fp.ResourceOwner()] = struct{}{}
-	}
-
-	rss := make([]string, 0, len(rs))
-
-	for k := range rs {
-		rss = append(rss, k)
-	}
-
-	return rss
-}

src/internal/data/data_collection_test.go

@@ -1,98 +0,0 @@
-package data
-
-import (
-	"testing"
-
-	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
-	"github.com/stretchr/testify/suite"
-
-	"github.com/alcionai/corso/src/pkg/path"
-)
-
-type mockColl struct {
-	p     path.Path
-	prevP path.Path
-}
-
-func (mc mockColl) Items() <-chan Stream {
-	return nil
-}
-
-func (mc mockColl) FullPath() path.Path {
-	return mc.p
-}
-
-func (mc mockColl) PreviousPath() path.Path {
-	return mc.prevP
-}
-
-func (mc mockColl) State() CollectionState {
-	return NewState
-}
-
-func (mc mockColl) DoNotMergeItems() bool {
-	return false
-}
-
-type CollectionSuite struct {
-	suite.Suite
-}
-
-// ------------------------------------------------------------------------------------------------
-// tests
-// ------------------------------------------------------------------------------------------------
-
-func TestCollectionSuite(t *testing.T) {
-	suite.Run(t, new(CollectionSuite))
-}
-
-func (suite *CollectionSuite) TestResourceOwnerSet() {
-	t := suite.T()
-	toColl := func(t *testing.T, resource string) Collection {
-		p, err := path.Builder{}.
-			Append("foo").
-			ToDataLayerExchangePathForCategory("tid", resource, path.EventsCategory, false)
-		require.NoError(t, err)
-
-		return mockColl{p, nil}
-	}
-
-	table := []struct {
-		name   string
-		input  []Collection
-		expect []string
-	}{
-		{
-			name:   "empty",
-			input:  []Collection{},
-			expect: []string{},
-		},
-		{
-			name:   "nil",
-			input:  nil,
-			expect: []string{},
-		},
-		{
-			name:   "single resource",
-			input:  []Collection{toColl(t, "fnords")},
-			expect: []string{"fnords"},
-		},
-		{
-			name:   "multiple resource",
-			input:  []Collection{toColl(t, "fnords"), toColl(t, "smarfs")},
-			expect: []string{"fnords", "smarfs"},
-		},
-		{
-			name:   "duplciate resources",
-			input:  []Collection{toColl(t, "fnords"), toColl(t, "smarfs"), toColl(t, "fnords")},
-			expect: []string{"fnords", "smarfs"},
-		},
-	}
-	for _, test := range table {
-		suite.T().Run(test.name, func(t *testing.T) {
-			rs := ResourceOwnerSet(test.input)
-			assert.ElementsMatch(t, test.expect, rs)
-		})
-	}
-}