i965: Make unify_interfaces not spread VARYING_BIT_TESS_LEVEL_*.
This is harmless today because gl_TessLevelInner/Outer in the TES is
currently treated as system values. However, when we move to treating
them as inputs, this would cause a bug: with no TCS present, it would
propagate TES reads of VARYING_SLOT_TESS_LEVEL into the VS output VUE
map slots. This is totally bogus - those don't even exist in the VS.
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>