sim: build: remove various obsolete generation dep variables

sim: build: remove various obsolete generation dep variables

These manual settings were necessary when we weren't doing automatic
header dependency tracking.  That was changed a while ago, and we use
automake now to do it all for us.  As a result, many of these vars
aren't even referenced anymore.

Further, some of the source file generation (e.g. .c files, or igen,
or cgen outputs) were moved to the common automake build, and it takes
care of dependency tracking for us with the object files.