Purge legacy HTIF things

The SCR file is gone, too, because it was tightly coupled.  The
general concept could be revived as a module that somehow connects
to the debug module.

vsim/Makefrag

@@ -38,7 +38,6 @@ VCS_OPTS = -notice -line +lint=all,noVCDE,noONGS,noUI -error=PCWM-L -timescale=1
 	-CC "-std=c++11" \
 	-CC "-Wl,-rpath,$(RISCV)/lib" \
 	-CC "-include $(consts_header)" \
-	-CC "-include $(scr_header)" \
 	-e vcs_main \
 	$(RISCV)/lib/libfesvr.so \
 	$(sim_dir)/libdramsim.a \