gofer 1.0.10 requires simplejson only on el5

python-simplejson has not been built for EL7 for all aches.  jmontleo was running into an issue and requested that gofer relax its requirement.  Users wanting the better performance provided by simplejson for both pulp and gofer can still optionally install it.  It's just not required.

The tarball was updated to do:

```
try:
  import simplejson as json
except ImportError:
  import json
```

Nothing else changed.