i965: Delete bogus assertion in emit_gs_input_load().

This looks like leftover cruft from an earlier attempt at writing
point size hacks.  Each vertex has its own copy of gl_PointSize,
so accessing any vertex other than 0 would cause this to fail.

The tests seem to work fine without it.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

src/mesa/drivers/dri/i965/brw_fs_nir.cpp

@@ -1991,7 +1991,6 @@ fs_visitor::emit_gs_input_load(const fs_reg &dst,
       /* This input was pushed into registers. */
       if (is_point_size) {
          /* gl_PointSize comes in .w */
-         assert(imm_offset == 0);
          bld.MOV(dst, fs_reg(ATTR, imm_offset + 3, dst.type));
       } else {
          for (unsigned i = 0; i < num_components; i++) {