Revert "UniStore: Add folder to the SQL backend" (#95966)

Revert "UniStore: Add folder to the SQL backend (#95671)"

This reverts commit f075662696.

pkg/storage/unified/sql/testdata/sqlite--resource_insert-simple.sql

@@ -5,7 +5,6 @@ INSERT INTO "resource"
         "resource",
         "namespace",
         "name",
-        "folder",
         "previous_resource_version",
         "value",
         "action"
@@ -16,7 +15,6 @@ INSERT INTO "resource"
         'rr',
         'nn',
         'name',
-        'fldr',
         123,
         '[]',
         'ADDED'