Remove wrongly added column on migration test fixtures (#23456)

Fix https://drone.gitea.io/go-gitea/gitea/69418/3/8
Migration fixtures are in `models/migrations/fixtures`, every folder
will be used only by the test with the same name.
For `Test_DeleteOrphanedIssueLabels`, the fixture should keep consistent
as the database structure at that time. So the newly added `exclusive`
is not right. Just revert the change in
https://github.com/go-gitea/gitea/pull/22585/files#diff-f8db9cbbaa10bf7b27eb726884454db821a4b4f8cb9a0d50435555908761bbcb

Author: lunny

models/migrations/fixtures/Test_DeleteOrphanedIssueLabels/label.yml

@@ -4,7 +4,6 @@
   org_id: 0
   name: label1
   color: '#abcdef'
-  exclusive: false
   num_issues: 2
   num_closed_issues: 0
 
@@ -14,7 +13,6 @@
   org_id: 0
   name: label2
   color: '#000000'
-  exclusive: false
   num_issues: 1
   num_closed_issues: 1
 -
@@ -23,7 +21,6 @@
   org_id:  3
   name: orglabel3
   color: '#abcdef'
-  exclusive: false
   num_issues: 0
   num_closed_issues: 0
 
@@ -33,7 +30,6 @@
   org_id: 3
   name: orglabel4
   color: '#000000'
-  exclusive: false
   num_issues: 1
   num_closed_issues: 0
 
@@ -43,6 +39,5 @@
   org_id: 0
   name: pull-test-label
   color: '#000000'
-  exclusive: false
   num_issues: 0
   num_closed_issues: 0