Stop supplying DIB_RELEASE

dib already picks DIB_RELEASE out of the env, and us setting a default
subverts its ability to do the right thing in elements. Similarly,
the DIB_IMAGE_NAME is both not a dib env var and was not being used, nor
was DIB_IMAGE_FILENAME.

Change-Id: I0522bad3a4be6d81d225fec37a08c7c71a65fe4d
Merge "Stop supplying DIB_RELEASE"