From the previous link, it is clear that ESH or LRC modules with DS14mk2FC are no longer supported.
The issue is that the FAS250 uses an integrated EFH module (see sysconfig output for Shelf 1). From this page: https://now.netapp.com/Knowledgebase/solutionarea.asp?id=ntapcs11615, it states that the Embedded Filer Hear (EFH) has an LRC module, which makes matters rather unclear. Is the FAS250 system shown above compatible with the GDR 7.3.3 release?
The FAS250 shelf is MK2, but you are right the EFH is considered and LRC. It is supported for 7.3 though as well as the FAS270 which uses the same onboard module. The download page gives 7.3.3 and 7.3.4 options supported for the FAS250 so an exception is made for the EFH. I would run an upgrade advisor on the system before doing an upgrade (from the my autosupport page) to confirm enough free space (3% free in each aggregate). I would also probably upgrade to 7.2 then 7.3 since if any issue with 7.3 you can't revert back to 7.0 (we can only revert 2 major releases)