sim: mcore: drop watchpoint/dumpmem/clearstats support

sim: mcore: drop watchpoint/dumpmem/clearstats support

In preparation for converting to the common memory framework, the custom
commands get in our way.  But when we realize that gdb support has been
dropped for mcore, it makes things a bit easier: the main runner does not
let you run arbitrary commands once simulation starts.

So lets disable watchpoint support until it can be converted to the common
watchpoint logic.  There's already an ifdef to let us do that.

We straight up drop support for the dumpmem command (no other sim supports
this, and if it's a feature people want, we can add a common func) and the
clearstats command (not a big deal -- just restart your simulation).

We leave in place the verbose check points as a follow up commit will cut
that over to common logic.