i965: Remove bad assert on isl_format

translate_tex_format() asserted that isl_format != 0. But 0 is a valid
format, ISL_FORMAT_R32G32B32A32_FLOAT.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/mesa/drivers/dri/i965/brw_surface_formats.c

@@ -575,7 +575,6 @@ translate_tex_format(struct brw_context *brw,
    }
 
    default:
-      assert(brw_isl_format_for_mesa_format(mesa_format) != 0);
       return brw_isl_format_for_mesa_format(mesa_format);
    }
 }