spearmint: Remove two unused ET bmodel variables (OpenGL2)

Already done for OpenGL1 in f4e2669e9a1b867bd42d1fa416dd6fc909ad33c1.
spearmint: Add marks on brush models

Extend R_MarkFragments to project marks onto brush models.

Projecting on to sides facing toward or away from direction platform
is moving often doesn't work. Top and bottom of vertical mover.
Sides of horizontal mover.

Tell CGame what bmodel the mark is on and specify bmodel for
trap_R_AddPolyToScene so that the mark moves with the brush model.
The vertexes are in bmodel local space instead of world space which
broke mark texture coords.

Modified the CGame API to have mark projection direction and bmodel
origin/axis to fix texture coords.

I'll probably remove bmodel origin/axis from markFragment_t later, cgame
knows them. Although knowing whether to use current or last frame bmodel
origin/axis to match renderer is probably slightly complicated. Ideally
the renderer would always have the current data. So I may look into
fixing that instead, which probably needs to be done anyway.

7 lines are based on ET's R_TransformDecalProjector, which probably
isn't eligible for copyright. Rotate and translate plane using axis
/ origin.