Remove extra index on snippets.project_id

Fixes https://gitlab.com/gitlab-org/gitlab/issues/37361

db/migrate/20191014132931_remove_index_on_snippets_project_id.rb

@@ -8,10 +8,13 @@ class RemoveIndexOnSnippetsProjectId < ActiveRecord::Migration[5.2]
   disable_ddl_transaction!
 
   def up
-    remove_concurrent_index :snippets, [:project_id]
+    remove_concurrent_index_by_name :snippets, 'index_snippets_on_project_id'
+
+    # This is an extra index that is not present in db/schema.rb but known to exist on some installs
+    remove_concurrent_index_by_name :snippets, :snippets_project_id_idx if index_exists_by_name? :snippets, :snippets_project_id_idx
   end
 
   def down
-    add_concurrent_index :snippets, [:project_id]
+    add_concurrent_index :snippets, [:project_id], name: 'index_snippets_on_project_id'
   end
 end