Revert "fix for #4049 (#4050)"

This reverts commit f3b2d2eb20.

src/oscar/apps/catalogue/expressions.py

 from django.db.models.expressions import Subquery
 
 EXPAND_UPWARDS_CATEGORY_QUERY = """
-(SELECT `CATALOGUE_CATEGORY_JOIN`.`id` FROM `catalogue_category` AS `CATALOGUE_CATEGORY_BASE`
-LEFT JOIN `catalogue_category` AS `CATALOGUE_CATEGORY_JOIN` ON (
-    `CATALOGUE_CATEGORY_BASE`.`path` LIKE `CATALOGUE_CATEGORY_JOIN`.`path` || '%%%%'
-    AND `CATALOGUE_CATEGORY_BASE`.`depth` >= `CATALOGUE_CATEGORY_JOIN`.`depth`
+(SELECT "CATALOGUE_CATEGORY_JOIN"."id" FROM "catalogue_category" AS "CATALOGUE_CATEGORY_BASE"
+LEFT JOIN "catalogue_category" AS "CATALOGUE_CATEGORY_JOIN" ON (
+    "CATALOGUE_CATEGORY_BASE"."path" LIKE "CATALOGUE_CATEGORY_JOIN"."path" || '%%%%'
+    AND "CATALOGUE_CATEGORY_BASE"."depth" >= "CATALOGUE_CATEGORY_JOIN"."depth"
 )
-WHERE `CATALOGUE_CATEGORY_BASE`.`id` IN (%(subquery)s))
+WHERE "CATALOGUE_CATEGORY_BASE"."id" IN (%(subquery)s))
 """
 
 
 EXPAND_DOWNWARDS_CATEGORY_QUERY = """
-(SELECT `CATALOGUE_CATEGORY_JOIN`.`id` FROM `catalogue_category` AS `CATALOGUE_CATEGORY_BASE` 
-LEFT JOIN `catalogue_category` AS `CATALOGUE_CATEGORY_JOIN` ON (
-    `CATALOGUE_CATEGORY_JOIN`.`path` LIKE `CATALOGUE_CATEGORY_BASE`.`path` || '%%%%' 
-    AND `CATALOGUE_CATEGORY_BASE`.`depth` <= `CATALOGUE_CATEGORY_JOIN`.`depth`
-) 
-WHERE `CATALOGUE_CATEGORY_BASE`.`id` IN (%(subquery)s))
+(SELECT "CATALOGUE_CATEGORY_JOIN"."id" FROM "catalogue_category" AS "CATALOGUE_CATEGORY_BASE"
+LEFT JOIN "catalogue_category" AS "CATALOGUE_CATEGORY_JOIN" ON (
+    "CATALOGUE_CATEGORY_JOIN"."path" LIKE "CATALOGUE_CATEGORY_BASE"."path" || '%%%%'
+    AND "CATALOGUE_CATEGORY_BASE"."depth" <= "CATALOGUE_CATEGORY_JOIN"."depth"
+)
+WHERE "CATALOGUE_CATEGORY_BASE"."id" IN (%(subquery)s))
 """