Update v1/images DELETE so it returns empty body.

Fixes an issue in the v1/images controller where a delete
response would contain a 'null' string instead of an empty
request body.

Fixes LP Bug #1098651.

Change-Id: I1a6610fe92e3a7f1221ca6f3e5f9e2c5e6130fbe
Merge "Update v1/images DELETE so it returns empty body."