Fix frv-elf sim, default hardware to off.

Fix frv-elf sim, default hardware to off.

At 2974be626, frv-elf fails at the dv_sockser_install declaration in
sim/frv/tconfig.in.  But, with the trivial #include's added (see other
sims tconfig.in, like cris or mn10300), it *still* fails building
sim/frv/devices.c because of a missing UART_INCHAR_ADDR.  I have no
insight into what'd be a valid value, except that there's a definition
in m32r, which was probably used as a template with frv not finished.
Simulated hardware should not have been be enabled, and was indeed not
enabled by default before 94c63d78f (2013-03-23), where it seems to
have been enabled for no simulator-specific reason.  Except
dv-sockser.o wasn't enabled even then: sim/frv/config.in wasn't
regenerated, so HAVE_DV_SOCKSER was never defined.  Maybe people were
fooled by this in sim/frv/Makefile.in at that time (these two lines
were later deleted, in 73e76d20):
CONFIG_DEVICES = dv-sockser.o
CONFIG_DEVICES =
(As it seems people have missed it before: the second line overrides
the first...)  I'm guessing these lines were part of the
never-completed hardware-support.  Commit 73e76d20 attempted to move
the imagined dv-sockser.o from $(CONFIG_DEVICES) to $(frv_extra_objs)
but missed that AC_SUBST would only affect @frv_extra_objs@ (not
$(frv_extra_objs) per se) so nothing happened regarding sockser:
dv-sockser.o was not compiled and HAVE_DV_SOCKSER was not defined.
I'm removing the $(frv_extra_objs) too, to avoid confusion.  The best
action seems to be disabling all hardware support by default again
until a specific sim maintainer finishes the work.
Make check-sim for frv-elf shows no failures after this.

sim/frv:
	* configure.ac: Default simulator hardware to off again.  Remove
	dead frv_extra_objs substitution.
	* configure: Regenerate.
	* Makefile.in: Remove unused frv_extra_objs.