EZP-22408 : regression test for related content removal bug
EZP-22408: on deleting Content cleanup field data of reversely related Content
EZP-22408: on Content delete clear SPI cache of reversely field related Content
Merge pull request #993 from ezsystems/fix-EZP-22408-relation-ref

Fix EZP-22408: Deleting a content does not remove references to this content in relation(list) fields