st/mesa: remove redundant st_context::vp,tcp,tep,gp,fp,cp
What does this MR do and why?
st/mesa: remove redundant st_context::vp,tcp,tep,gp,fp,cp
Use ctx->XXProgram._Current instead of the st_context variables.
Also, the st_release_program calls were redundant. The same code is
invoked when mesa/main unreferences shaders.