Don't check password stores exist on Concourse
Don't check password stores exist on Concourse

These lines checking for the existence on disk of
`PAAS_PASSWORD_STORE_DIR` and `PAAS_HIGH_PASSWORD_STORE_DIR` were
added to make the Makefile cleaner. However in practice this doesn't
work:

  1) Self-update pipeline run on Concourse will fail because it
     doesn't have those `pass` credential stores checked out;

  2) Engineers without the high pass store won't be able to interact
     with production.

alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf