draw: don't try to precalculate the pipeline output primitive

draw: don't try to precalculate the pipeline output primitive

We were previously calculating a value which was either the geometry
shader output primitive or the application's input primitive, and
passing that to the various front/middle/back components for use as
the ultimate rendering primtive.

Unfortunately, this was not correct -- if the vcache decomposition
path is active and geometry shaders are *not* active, we can end up
with a third primitive -- specifically the decomposed version of the
input primitive.

Rather than trying to precalculate this, just let the individual
components inform their successors about which primitive type they are
recieving.