Revert "Split ExtraConfig into compute + control"

We need to retain backwards compatibility, so this isn't the right
way to go with this.

Also - there is no need to add extra environment variables, as the
extra config data can just be written to the heat environment file.

This reverts commit fbd8039ac978f67926faeadd4b0d6a4c4010705a.

Change-Id: I6ec3593cdebba27625b1cb3c9da0a3bbfc907ea4