Fix PS3 backend removal (Cedric...)
When running elementary_test with ELM_ENGINE='buffer', we got a crash.
The removal of PS3 backend patch didn't remove ELM_SOFTWARE_PSL1GHT and
didn't shift the _elm_engines indexes.
ELM_SOFTWARE_DDRAW stayed at the index 13 (value NULL) instead of moving
to index 12.
A strcmp with NULL occurred, leading to the crash.
@cedric, I excuse you to not have run Exactness your code before pushing