remove conv.scm, disasm.scm; objcode->bytecode rename

remove conv.scm, disasm.scm; objcode->bytecode rename

* module/system/vm/Makefile.am:
* module/system/vm/conv.scm:
* module/system/vm/disasm.scm: Remove these modules, as their
  functionality is now in (language ...).

* libguile/objcodes.h:
* libguile/objcodes.c:
* module/system/vm/objcode.scm: Rename objcode->u8vector to
  objcode->bytecode.

* module/system/vm/frame.scm:
* module/language/bytecode/spec.scm: Fix for objcode->bytecode.

* scripts/disassemble:
* testsuite/run-vm-tests.scm: Fix for (system vm disasm) removal.

* module/system/repl/command.scm: Use the right disassembler.