[rv_dm,dv] Remove check from scoreboard about unmapped DTM reads

[rswarbrick]

The dout value here comes from pulp code in dmi_jtag_tap.sv (see the always_comb block that drives tdo_mux) and we'll almost get the BYPASS behaviour, but not quite. Since the correct behaviour of rv_dm doesn't really include an opinion about what happens here, let's ignore it.