i965/blorp/gen6: Remove dead code in hiz setup
i965/blorp/gen6: Remove dead code in hiz setup

Such as comment states for intel_miptree_hiz_buffer::mt, hiz_mt
only exists for gen6. In addition, intel_hiz_miptree_buf_create()
uses MIPTREE_LAYOUT_FORCE_ALL_SLICE_AT_LOD unconditionally.

Reviewed-by: Jason Ekstrand <68c46a606457643eab92053c1c05574abb26f861@jlekstrand.net>
Signed-off-by: Topi Pohjolainen <749697f19798b7f640b17221fd283b903825f071@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler