remove unused sfepy/solvers/petsc_worker.py
remove unused sfepy/solvers/petsc_worker.py

- see 125d59dd82c0f2e4c88031c7c58e2dfa255c8cf8

rc/sfepy,lokik/sfepy,BubuLK/sfepy,vlukes/sfepy,lokik/sfepy,vlukes/sfepy,sfepy/sfepy,vlukes/sfepy,lokik/sfepy,rc/sfepy,lokik/sfepy,BubuLK/sfepy,sfepy/sfepy,sfepy/sfepy,rc/sfepy,BubuLK/sfepy